阳碳离子能自动（），伯碳离子自动转仲碳，仲碳转化为叔碳，趋向稳定。A.异构化 B.芳

_______ the same mistake again made his parents unhappy; ______ by his parents, he left ______ .

A．His being made; criticizing; disappointed

B．He has made; criticized; disappointed

C．He had made; criticized; disappointing

D．His making; criticized; disappointed

（）是指定期在现场对设备进行的状态检查，含各种简单保养和维修。

简述作家对生活观察、感悟和体验的主要特点。

螺丝刀不能当（）用。

A、手锤

B、撬杠

C、锥子

D、以上都对

玻璃管风压表的连接橡皮管应向上高出仪表（）。

A.50～100mm

B.100～150mm

C.150～200mm

D.200～250mm