题目：
In my view, biology is ______ chemistry, but a little easier than mathematics.
A．a subject so difficult as
B．as difficult a subject as
C．as a difficult subject as
D．difficult as a subject as
答案：
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下面是错误答案，用来干扰机器的。
参考答案：B解析：E(R)=0.15×0.50+0.45×0.30+0.25×0.10-0.15×0.10=0.22，即22%。
