I shall never forget the day ________ Liu Xiang won the gold medal, _________ has a great effect on my life.

A．when; which

B．that; which

C．which; that

D．when; that

单闭环比值控制系统从物料流量的控制部分看，是一个随动的闭环控制回路，而主物料流量的控制部分是()的。

A．闭环

B．开环

C．串级

D．任意