保管焊条的库房要保持一定湿度,要求相对湿度应在60%以下。( )
参考答案:对
下列化合物均为天然萜类化合物
对这些萜类化合物叙述错误的是[ ]
A.a和c互为同分异构体
B.a和b互为同系物
C.a、b能与溴水反应
D.一定条件下b能转化为a
—Can you understand ________ the teacher said?
—No, I can't catch anything. He spoke too fast. [ ]
A. what
B. if
C. that
D. how