A:SiH4> PH3>H2S>HCl
B:HF>HCl>HBr>HI
C:NH3>PH3>AsH3>HF
D:PH3>AsH3> H2S>HCl
—I'm trying to keep my cool because we've been together ________ three years.
用显微镜进行观察研究时,材料必须是( )。