In the first test each subject sat before a computer screen and pressed a key as soon as

In the first test, each subject sat before a computer screen and pressed a key as soon as he or she recognized a target letter among a grouping of 96. In this simple test, smokers, deprived smokers and nonsmokers performed equally well.

The next test was more complex, requiring all to scan sequences of 20 identical letters and respond the instant one of letters transformed into a different one. Nonsmokers were faster, but under the stimulation of nicotine active smokers were faster than deprived smokers.

In the third test of short - term memory, nonsmokers made the fewest errors, but deprived smokers committed fewer errors than active smokers.

The fourth test required people to read a passage, then answer questions about it. Nonsmokers remembered 19 percent more of the most important information than active smokers, and deprived smoker bested those who had smoked a cigarette just before testing. Active smokers tended not only to have poorer memories but also had trouble separating important information from insignificant details.

As our tests became more complex, sums up Spilich, "nonsmokers performed better than smokers by wider and wider margins." He predicts, "smokers might perform. adequately at many jobs——until they got complicated. A smoking airline pilot could fly adequately if no problems arose, but if something went wrong, smoking might damage his mental capacity."

The purpose of George Spilich"s experiments is _________.

A．to test whether smoking has a positive effect on the mental capacity of smokers

B．to show how smoking damages people"s mental capacity

C．to prove that smoking affects people"s regular performance

D．to find out whether smoking helps people"s short-term memory

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