Passage 21

It is impossible to answer the question, “Who built the first canal?” Perhaps some people long ago, living in a dry country, discovered that they could dig ditches to irrigate(灌溉)their fields with river water. And, naturally, in the days when boats were the most important means of transport, canals were the easiest means of reaching a place that was not on a river, but was at the same level as a river. Furthermore, a ditch joining two rivers proved both easy and time-saving for boat travel.
Today, most countries in the world have canals. Even in the twentieth century, goods can be moved more cheaply by boat than by any other means of transport. Some canals, such as the Suez or the Panama, save ships weeks of time by making their voyage a thousand miles shorter.
The size of a canal depends on the king of boats going through it. The canal must be wide enough to permit two of the largest boats using it to pass each other easily. It must be deep enough to leave about two feet of water beneath the bottom of the largest boat using the canal.
In places where it does not rain very often, irrigation canals drain water from rivers or lakes and carry it to fields. Sometimes artificial lakes, such as the lake behind the Aswan Dam on the Nile River, provide the irrigation water.
In places where there is too much water, canals can drain the water off the land for use in farming, In Holland, acres and acres of land have been drained in this way. Since much of this drained land is below sea level, the water in the canals has to be pumped up to sea level.
Many countries have built canals near the coast, and parallel to the coast. These waterways make it possible for boats to travel between ports along the coast without being exposed to the dangers of the open sea.

1.Where were canals first built?

A. Suez 

B. Panama

C. Holland 

D. No one knows

2.A canal must be deep enough to leave how many feet of water beneath the bottom of the largest boat using the canal?

A. One foot of water 

B. Two feet of water

C. Five feet of water

D. Ten feet of water

3.The Aswan Dam was built primarily for what purpose?

A. Navigation 

B. Irrigation

C. Drainage

D. Electricity

4.Compared to other means of water transport, canal boats are___________.

A. cheaper and sometimes faster

B. more expensive, but faster

C. cheaper, but more dangerous

D. more expensive and slower

5.Are canals ever built parallel to the sea coast?

A. No, because boats can use the sea

B. Yes, to protect boats from storms.

C. No, because the sea can flood the canals

D. Yes, to protect boats from attacks.