下列分子中有3个原子核的是( )
A.HF
B.NH3
C.H2O
D.CH4
答案:C
I like English very much. I never miss a to practice English with foreigners.
A.subject
B.mistake
C.chance
D.space
平均来说,海水的盐度为()。
A、9.2%
B、7.7%
C、5.9%
D、3.5%