Chuyển sang câu bị động các câu sau:
1.Our English teacher may give an exam to day.
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2.You may forget the rules quickly.
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3.Janet used to study the lessons repeatedly.
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4.Ben must win the competition.
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5.The doctor can't persuade her.
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6.The students have to learn History.
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7.Tom must open the window.
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8.How can we solve that problem?
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9.You must not touch this button during the experiment.
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10.We should call the police at once after the accident.
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11. You shouldn't make fun of the poor.
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12.My sister used to open a shop 3 years ago.
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13.We have to end this quarred.
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14.You ought to help her.
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15.You must keep the secret forever.
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