At the meeting, they sat very ________ and had a ________ talk, but I didn't know what they were

talking about. [ ]

A. close; close 

B. closely; close

C. close; closely  

D. closely; closely

酸碱再生液在交换器内的空塔流速，以（）m/h为宜。

A.1~3

B.2~4

C.4~8

D.8~10