It was ____terrible earthquake and _____number of people who were killed reached more than 20,000.

A．a; the

B．the; a

C．the; the

D．a; a

我国著名化学家徐辉碧教授根据众多的实验事实证明：硒元素（Se）与艾滋病有关．硒与硫有着相类似的性质，以下化学式属硒酸是（　　）

A．SeO₂

B．Na₂SeO₄

C．H₂Se

D．H₂SeO₄