It was 1969___ the American astronauts succeeded in landing on the moon.

A． that

B． when

C． on which

D． which

单圈弹簧管压力表的检修首先是（），然后观察整个刻度范围内误差的规律。

A、零点检查

B、示值检定

C、观察表有没有摩擦

D、量程检查