--- I didn’t invite him to the party but he came anyway and got completely drunk.

--- _______ he hadn’t come! The party could have been a success.

A．How come

B．Only if

C．What if

D．If only

能使污水中BOD5的净化率达到25%～40%的污水处理流程为（）。

A．一级处理

B．二级处理

C．三级处理

D．特级处理