1.— Could I cross the street here? — Of course you____. A. could B. can C. be able to D. will 思路点拨： 此句中的could 表示委婉的语气，而不是表示过去时态。故回答时应用can，表示能够干某事。 2. Some people think trees _____ on Tree Planting Day only. A. should be planted B. should plant C. should be planting D. be planted 思路点拨：表“义务”和“应该”时，用should。情态动词的被动语态为：情态动词+ be +done。

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