---What is the boy doing?---He happily.A swims B swam C has swum D is swimming

发布时间：2020-08-20 20:47:43

---What is the boy doing?
---He      happily.
A swims    B swam    C has swum    D is swimming

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解析：
问句是：What is the boy doing?说明是用现在进行时，选D。
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