Câu tường thuật - dạng câu kể 

S + said to / told + O + (that) + S + V (lùi thì)

S + said + (that) + S + V (lùi thì)

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HTĐ ⇒ QKĐ

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Đáp án: Mary told Tom that his sister worked very hard.

`color{orange}{~MiaMB~}`

`answer:` Mar said to Tom her sister worked very hard

`-` Câu tường thuật:
S + said to sb + (that) + S + V(lùi thì)

`-` lùi thì: HTĐ `->` QKĐ