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问题 单项选择题

血浆pH主要决定于下列哪种缓冲对（）

A.KHCO3／H2CO3

B.NaHCO3／H2CO3

C.K2HPO4／KH2PO4

D.Na2HPO4／NaH2PO4

E.Na3CO3／NaHCO3

答案

参考答案：B

选择题

—Tom wants to know if you ________ a picnic next Sunday.

—Yes. But if it ________， we'll visit the museum instead.

A．will have; will rain

B．have; rains

C．have; will rain

D．will have; rains
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选择题

The students of Senior 3 are now under great pressure for it will be just one year ______ they take the Entrance Examination.

A．since

B．after

C．before

D．when
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