齿轮装配精度要求较高时，一般用（）检查齿侧间隙
A．百分表
B．压铅法
C．涂色法
D．千分尺
参考答案：A
The house which _____ four hundred years ago is still in good condition. [ ]
A.dates back to
B.dated back
C.dated from
D.dated back from
写出信号报警和联锁系统产生误动作的原因
