They are playing happily on the playground(are playing happily） ＿＿ they＿ on the playground
问题描述：
They are playing happily on the playground(are playing happily） ＿＿ they＿ on the playground
答
Are playing
答
What are doing
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答
What are,doing
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答
【What're 】they【doing】on the playground ?
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