◎ 题干
—Jack.  All the young trees____at once.        
—OK.  I'll do it at once.
[     ]
A. must be watered
B. must water
C. must be watering
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“—Jack.All the young trees____at once. —OK.I'll do it at once.[ ]A. must be watered B. must water C. must be watering…”主要考查了你对  【情态动词】【被动语态】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。