Đáp án:

`1,` There's no necessary for children to study too much.

- S + needn't + V $=$ There's no necessary + for sb + to V

`->` Ai không cần làm gì đó - Không cần thiết cho ai làm gì

`2,` The yard was being swept by the children.

- Bị động QKTD $(+)$ S + was / were + being + V3 / PII ( by O ).

- The yard là chủ ngữ số ít `->` Chia was

`3,` Had I known she was sick, I would have visited her.

- Đảo ngữ CĐK loại `3:` Had + S + V3 / PII`,`S + would / could / might + V

`->` Diễn tả sự việc không có thật ở quá khứ

1, There's no necessity for children to study too much

S+needn't+ V= There's no necessity for sb to V: ko cần thiết phải lmj

2. The yard is the place where the children were sweeping

Where là đtqh that thế cho danh từ phía trước có chức năng làm trạng ngữ trong câu

3. Had I known she was sick, I would have visited her

Đảo ngữ câu điều kiện loiaj 3: Had+ S+ Pii, S+ would have Pii