采用插入式振捣混凝土时,其操作应()。
A、慢插慢拔
B、慢插快拔
C、快插慢拔
D、快插快拔
参考答案:C
I’m afraid you have to get your room ____________. It’s too dirty and messy!
A. cleaning B. to clean C. cleaned C. to be cleaned
三相异步电动机的转速取决于电源频率和极对数,而与转差率无关