—I paid him 200 yuan for the sneakers.

—Oh, he charged you too much. You _________ them with half the money.

A．could have bought

B．needn’t have bought

C．must have bought

D．wouldn’t have bought

使用正弦规时，将正弦规放在平板上，圆柱之一与平板接触，另一圆柱下垫以量块，则正弦规的工作平面与平板间组成一角度。其关系式为：（）。

A.sinа=h/L

B.sin2а=h/L

C.cosа=2h/L

D.cosа=h/L