用HCl中和Na2CO3溶液分别至pH=10.5和pH=7.0时，溶液中各有哪些组分？其主要组分是什么？H2CO3的Ka1=4.2×10-7，Ka2=5.6×10-11
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Is there ____“s”in the end of the word?
A. an
B. a
C. the
D. /
Mr. Wang is ____honest man.
A. an
B. a
C. the
D. /
He is ____university student.
A. a
B. an
C. the
D. /
____ book is very useful. I bought it from____unknown little town.
A, a
B. The, a
C. The, the
D. The, an
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