—Have you known each other for long?

—Not very long, 　　　we started to work in the company.

A．after

B．before

C．when

D．since

对高压容器、大型容器以及安全泄放量较大的中低压容器安全阀最好选用（）

A.先导式安全阀

B.全启式安全阀

C.微启式安全阀