离心泵如果发生严重无声震动，其主要原因是：（）
A.轴承磨损严重
B.吸入管路堵塞严重
C.涡壳内有异物
D.B+C
参考答案：D
阅读理解。
根据表格内容，判断正（T）误（F）。
( )1. Wang Ying doesn’t like vegetables.
( )2. Mary and Gao Min eat fruit for supper.
( )3. Gao Min has meat, vegetables and soup for lunch.
( )4. Mary likes fruit better (更喜欢) than vegetables.
( )5. They have different foods for lunch.
A little knowledge is _______, because it can cause people to think they are more expert than they really are.
A．expensive
B．ordinary
C．precious
D．dangerous
