Đáp án + Giải thích bước giải:

1. It’s important to keep the environment clean

→ important + to-V: quan trọng

2. The time machine will be shown to the public when they finish it

→ Câu bị động thì TLĐ: S + will be + V3/ed + ...

3. He was delighted to receive his aunt's letter.

→ Chỉ người nên dùng Ved

→ delighted to: vui mừng

4. People recycle old car tires to make shoes and sandals

→ Câu chủ động thì HTĐ: S + Vs/es

5. I’m very sad not to be accepted in that group.

→ QKĐ →  not to be = wasn't

→ Chỉ người nên dùng Ved

6. I haven’t spoken to her for two years

→ thì HTHT: S + have/has + V3/ed + ...

1. Keeping the environment clean is very important

=> It’s important to keep the environment clean

2. They will show the time machine to the public when they finish it.

=>1. The time machine will be shown to the public when they finish it.

3. He was delighted to receive his aunt’s letter.

=>He was delighted that he received his aunt’s letter.

4. Old car tires are recycled to make shoes and sandals.

=>People recycle old car tires to make shoes and sandals.

5. I’m very sad that I wasn’t accepted in that group.

=>I’m very sad not to be accepted in that group.

6. It’s three years since I last spoke to her.

=>I haven’t spoken to her for two years.