pH 值为9.40的一元弱碱溶液中OH- 离子浓度为 ( )。
A. 4.0×10-10 mol·L-1
B. 2.5×10-9 mol·L-1
C. 4.0×10-6 mol·L-1
D. 2.5×10-5 mol·L-1
---Who is the man _______ was talking to our English teacher?---Oh! It’s Mr Baker, our maths teacher.
A. he
B. that
C. whom
D. which
I hate the people ________ don’t help others when they are in trouble.
A. who
B. which
C. they
D. there
This is the place _____I have ever visited.
A. there
B. when
C. where
D. which
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