水准仪是测量()的常用仪器，通常使用光学水准仪。

A.两点之间垂直高差

B.两点之间水平距离

C.两点之间水平角度

D.两点之间垂直角度

- As middle school students, we should study hard for the future.

- I think so. _____ we study now, _____ future we’ll have.

A．The hard, the good

B．The harder, the better

C．The hardest, the best

D．The hard, the best