往复泵的流量调节只能采用调节活塞的冲程,才能达到调节流量的目的。()
参考答案:错
解析:可以采用调节活塞的冲程和在泵出口处装旁路管线到进口处达到调节流量的目的。
He had hardly finished his meal ________ a familiar voice came to his ears.[ ]
A. why
B. where
C. when
D. while
配制pH=7的缓冲溶液,应选用: