17. Inspection system X and inspection system Y， though based on different principles， each detect all product flaws but they each also erroneously reject three percent of flawless products.Since false rejections are very costly， money will by saved by installing both systems， instead of either one or the other， and rejecting only products found flawed by both.

　　（A） The three percent of flawless products that system X rejects are not all the same products， piece for piece， that system Y erroneously rejects.

　　（B） It is less costly to accept a flawed product than to rejects a flawless one.

　　（C） In their price range. System X and Y are the least error-prone inspection systems on the market.

　　（D）Whichever system performs the second inspection needs to inspect only products not rejected by the first system.

　　（E） Any way of detecting flaw， other than by using either system X or systemy， requires complete disassembly of the products.

　　18. Statistics over four consecutive years showed that four percent more automobile accidents happened in California during the week following the switch to daylight saving time and during the week following the switch back to standard time than occurred the week before each event. These statistics show that these time changes adversely affect the alertness of California divers.

　　The conclusion in the argument above is based on which of the following assumptions？

　　（A） Drivers in California as well as those in the rest of the United States have similar driving patterns.

　　（B） The observed increases in accident rates are due almost entirely to an increase in the number of minor accidents.

　　（C） Four years is not a sufficiently long period of time over which to judge the phenomenon described.

　　（D） There are no other factors such as school vacations or holiday celebration that cause accident rates to rise during these weeks.

　　（E） A time change at any other time of years would not produce a similar increase in accident rates.