对于故障不直接危及使用安全而且仍可保持基本功能的设备采用（）维修方式。
A．定时
B．定期
C．视情
D．事后
参考答案：D
____________ many times, but he still couldn’t understand it.
A．Though he had been told
B．Having been told
C．Having told
D．He had been told
向钢水中加入硅铁合金，会造成钢水温度（）。
A.升高
B.降低
C.不变
