AIDS is said __________ the biggest health challenge to both men and women in that area over the past few years.

A．that it is

B．to be

C．that it has been

D．to have been

脱水塔操作中，塔底温度过低会使（）。

A.溶剂油含丁二烯

B.溶剂油不含丁二烯

C.溶剂油含水