—Perhaps we can't arrive at the bus station on time.

—________.We still have forty minutes.

A．Yes, you are right

B．Not at all

C．What a pity　

D．Take it easy

石英表中石英的主要成分是SiO₂，其中硅元素的化合价为（　　）

A．+1

B．+2

C．+3

D．+4