Americans are nervous ____________ the prospect of a nuclear-armed Iran, but also worry

__________ the ability of the United States and the United Nations to deal with the situation.

A．about; about

B．to; about

C．for; about

D．for; for

气相色谱－质谱联用仪的（）对载气中氧气的分压要求比较苛刻。

A.离子源

B.质量分析器

C.检测器