CRH1A型动车组受电弓的弓头和上臂之间安装了（）个扭簧。
A.1
B.2
C.3
D.4
参考答案：B
— How long have you _______ this book?
— About ten days. I _______ it last month.
A．bought, bought
B．bought, buy
C．had, bought
D．had, have bought
调整光比，主要采用改变光源与被摄者之间的（）来实施。
A.角度
B.方向
C.距离
D.背景
