—Your daughter has two children, doesn’t

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问题选择题

—Your daughter has two children, doesn’t she?

—That’s right; she for ten years.

A．has not married

B．married

C．has married

D．has been married

答案

答案：D

填空题

把在空气中久置的铝片5.0 g 投入盛有500 mL 0.5 mol ·L^－1硫酸溶液的烧杯中，该铝片与硫酸反应产生氢气的速率与反应时间的关系可用如图曲线来表示，回答下列问题：

(1) 曲线由O →a段不产生氢气的原因是___________________________；有关反应的化学方程式为_________________ ；

(2) 曲线a→c段，产生氢气的速率增加较快的主要原因是____________________________；

(3)曲线由c以后，产生氢气的速率逐渐下降的主要原因是____________________________；

(4)该反应若使用催化剂，可使H₂产量增多吗？______(填“会”或“不会”)。

选择题

He devoted most of his time to his research, believing his hard work would___sooner or later.

A．put off

B．take off

C．come off

D．pay off