1. If the water is contaminated, people will get more diseases.

if 1: If + HTĐ, S + will/can/shall ..  +V1 

2. He said that he had never seen that place before.

S + said + (that) + S+ V (lùi thì)

HTHT --> QKHT 

this --> that 

3. If he weren't late every day, he wouldn't lose his job.

If 2: If + QKĐ, S+ would / could  +V1

4. She said that she had decided to go on holiday in Singapore.

S + said + (that) + S+ V (lùi thì)

HTHT --> QKHT 

5. They said that they were playing chess then.

S + said + (that) + S+ V (lùi thì)

HTTD --> QKTD 

now --> then 

6. If they exercised regularly, their health would be very good.

If 2: If + QKĐ, S+ would / could  +V1

7. If I didn't have to help my mum, I could come.

If 2: If + QKĐ, S+ would / could  +V1

8. If he weren't late every day, he wouldn't lose his job.

If 2: If + QKĐ, S+ would / could  +V1

9. While I was having breakfast, the phone rang.

While + QKTD, QKĐ

10. We enjoy visiting museums when we have leisure time.

enjoy + Ving: thích 

11. If you don't stop swimming in that lake, you will have skin rashes.

if 1: If + HTĐ, S + will/can/shall ..  +V1 

12. Although the girl worked hard, her stepmother wasn't happy.

Although + clause, clause: mặc dù 

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