题目内容：
阅读短文，回答题：
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
参考答案：
答案解析：