设备的磨合期一般是指（）。
A、早期故障期
B、偶发故障期
C、耗损故障期
D、多发故障期
参考答案：A
________ with some research materials, he decided on three possible approaches in his experiment.
A．Preparing
B．Prepared
C．Having prepared
D．Prepare
变换坐标系有几种（）。
A、5
B、6
C、7
D、8
