—How ______ do you write to your mother —Twice a month.
A. [A] much
B. [B] soon
C. [C] often
查看答案
下列化合物在水溶液中，碱性最弱的是（）。
A. N(C2H5)3
B. NH(C2H5)2
C. NH3
D. (C2H5)4N+OH-
I'm sure he'll do all he can ______.
A. [A] for help
B. [B] to help
C. [C] for helping
—Did you remember ______ Ann —Oh no, I completely forgot.
A. [A] to phone
B. [B] phoning
C. [C] phone
Tom has ______ back the money he borrowed from me yesterday.
A. [A] brought
B. [B] given
C. [C] taken
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