问题描述：
情态动词的祈使句
把You must keep quiet in the reading room.
You cannot swim in the river.
My brother is able to ski.改为祈使句
再+个：You must not read in the sun.
把You must keep quiet in the reading room.
You cannot swim in the river.
My brother is able to ski.改为祈使句
再+个：You must not read in the sun.
问题解答：
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