问题描述：
we have to ____ everyone _____that keeping our city clean is our duty.
a.let;to know b.make;understand c.make;to understand d.have;to know
选哪个 为什么?
a.let;to know b.make;understand c.make;to understand d.have;to know
选哪个 为什么?
问题解答：
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