__in pairs is a very good way of learning.they stayed in the libr_英语解答

__in pairs is a very good way of learning.
they stayed in the library __ three hours
请具体说出原因,

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解答

选择呢?Learn不对Live和for1Awork Bworking Cworks DworkedB动词不能做主语。要变成动名词。动词不可以作主语啊？嗯