The subjects of the following studies are taken from the history of the Renaissance, and touch what I think the chief points in that complex, many-sided movement. I have explained in the first of them what I understand by the word, giving it a much wider scope than was intended by those who originally used it to denote that revival of classical antiquity in the fifteenth century which was only one of many results of a general excitement and enlightening of the human mind, but of which the great aim and achievements of what, as Christian art, is often falsely opposed to the Renaissance, were another result. This outbreak of the human spirit may be traced far into the middle age itself, with its motives already clearly pronounced, the care for physical beauty, the worship of the body, the breaking down of those limits which the religious system of the middle age imposed on the heart and the imagination. I have taken as an example of this movement, this earlier Renaissance within the middle age itself, and as an expression of its qualities, two little compositions in early French
computer-assisted instruction (CAI), a program of instructional material presented by means of a computer or computer systems.
The use of computers in education started in the 1960s. With the advent of convenient microcomputers in the 1970s, computer use in schools has become widespread from primary education through the university level and even in some preschool programs. Instructional computers are basically used in one of two ways: either they provide a straightforward presentation of data or they fill a tutorial role in which the student is tested on comprehension.
If the computer has a tutorial program, the student is asked a question by the computer; the student types in an answer and then gets an immediate response to the answer. If the answer is correct, the student is routed to more challenging problems; if the answer is incorrect, various computer
messages will indicate the flaw in procedure, and the program will bypass more complicated questions until the student shows mastery in that area.
There are many advantages to using computers in educational instruction. They provide one-to-one interaction with a student, as well as an instantaneous response to the answers elicited, and allow students to proceed at their own pace. Computers are particularly useful in subjects that require drill, freeing teacher time from some classroom tasks so that a teacher can devote more time to individual students. A computer program can be used diagnostically, and, once a student's problem has been identified, it can then focus on the problem area. Finally, because of the privacy and individual attention afforded by a computer, some students are relieved of the embarrassment of giving an incorrect answer publicly or of going more slowly through lessons than other classmates.
There are drawbacks to the implementation of computers in instruction, however. They are generally costly systems to purchase, maintain, and update. There are also fears, whether justified or not, that the use of computers in education decreases the amount of human interaction.
One of the more difficult aspects of instructional computers is the availability and development of software, or computer programs. Courseware can be bought as a fully developed package from a software company, but the program provided this way may not suit the particular needs of the individual class or curriculum. A courseware template may be purchased, which provides a general format for tests and drill instruction, with the individual particulars to be inserted by the individual school system or teacher. The disadvantage to this system is that instruction tends to be boring and repetitive, with tests and questions following the same pattern for every course. Software can be developed in-house, that is, a school, course, or teacher could provide the courseware exactly tailored to its own needs, but this is expensive, time-consuming, and may require more programming expertise than is available.
结冰条件的那道阅读理解我找到了，貌似是一道托福真或模拟题，见Deltas Key to the Next Generation TOEFL Test: Advanced Skill Google 图书结果 Nancy Gallagher - 2005 - Study Aids - 699 页
Two conditions are necessary for the formation of ice: the presence of water and temperatures below freezing. Ice in the atmosphere and on the ground can assume various forms, depending on the conditions under which water is converted to its solid state. Ice that forms in the atmosphere can fall to the ground as snow, sleet, or hail. Snow is an assemblage of ice pellets. Hail consists of rounded or jagged lumps of ice, often in layers like the internal structure of an onion. Ice also forms directly on the ground or on bodies of water, it may not form until late winter because there must be several months of low temperatures to chill such large amounts of water.
On puddles and small ponds, ice first freezes in a thin layer with definite crystal structure that becomes less apparent as the ice thickens. On lakes large enough to have waves, such as the Great Lakes, the first ice to form is a thin surface layer of slush, sometimes called grease ice, which eventually grows into small floes may freeze together into a fairly solid sheet of pack ice. Pack ice
may cover the entire lake or be restricted to areas near the shore.
Because water expands when it freezes, ice is less dense than liquid water and therefore floats rather than sinks in water. As ice floats on the surface of a lake, ocean, or river, it acts as an insulator and is thus important in maintaining the balance of the ecosystem. Without the insulating effect of floating ice sheets, surface water would lose heat more rapidly, and large bodies of water such as the Arctic Ocean and Hudson Bay might freeze up completely.
1. What condition is necessary for water in the atmosphere to change to its solid state?
A. A solid cloud cover that absorbs the sun's heat.
B. A weather forecast for snow, sleet, or hail
C. A position directly above a large body of water
D. A temperature below water's freezing point
2. Ice that forms in the atmosphere in the form of layered lumps is known as
B. pack ice
D. grease ice
3. Why does ice form later on very large bodies of water?
A Most large bodies of water are located at low elevations or low latitudes.
B. It takes several months of cold temperatures to cool a large body of water.
C. Large bodies of water are fed by underground springs of warmer water.
D. The waves on large bodies of water prevent the water from freezing quickly.
4. The word it in paragraph 3 refers to
5. Which of the following is an effect of the density of ice?
A. Ice that forms on large lakes has a greasy consistency.
B. Each ice crystal is unique, but all are six-sided structures.
C. Pack ice is restricted to areas near the shore of a lake.
D. Floating ice sheets prevent bodies of water from losing heat.
Although recent years have seen substantial reductions in noxious pollutants from individual motor vehicles， the number of such vehicles has been steadily increasing. Consequently， more than 100 cities in the United States still have levels of carbon monoxide， particulate matter， and ozonethat exceed legally established limits. There is a growing realization that the only effective way to achieve further reductions in vehicle emissions — short of a massive shift away from the private automobile — is to replace conventional diesel fuel and gasoline with cleaner-burning fuels such as compressed natural gas， liquefied petroleum gas， ethanol， or methanol.
All of these alternatives are carbon-based fuels whose molecules are smaller and simpler than those of gasoline. These molecules burn more cleanly than gasoline， in part because they have fewer， if any， carbon-carbon bonds and the hydrocarbons they do emit are less likely to generate ozone. The combustion of larger molecules， which have multiple carbon-carbon bonds involves a more complex series of reactions. These reactions increase the probability of incomplete combustion and are more likely to release uncombusted and photochemically active hydrocarbon compounds into the atmosphere. On the other hand， alternative fuels do have drawbacks. Compressed natural gas would require that vehicles have set of heavy fuel tanks — a serious liability in terms of performance and fuel efficiency — and liquefied petroleum gas faces fundamental limits on supply.