―Isn’t it hard to drive downtown to work?

—Yes, that’s why I ________ to work by train.

A．have been going

B．have gone

C．was going

D．will have gone

IQ＝100+15（X-）／SD是（）的计算公式。

A.比率智商

B.标准分数

C.标准差

D.离差智商