1. Mary wanted to buy a new watch but she didn't have enough money.

• Explanation: "but" is used to show a contrast between two ideas. Mary wanted to buy a watch, but she couldn't because she didn't have enough money.

2. Is this man older or younger than you?

• Explanation: "or" is used to present choices or alternatives. The question is asking whether the man is older or younger than you.

3. Jane tried hard for the exam and she passed it.

• Explanation: "and" is used to connect two similar ideas. Jane tried hard and succeeded in passing the exam.

4. She speaks clearly although she is only two years old.

• Explanation: "although" is used to show a contrast between two ideas, even though the second idea is surprising or unexpected. Despite being only two years old, she speaks clearly.

5. We went to Da Lat and had a nice time.

• Explanation: "and" is used to connect two similar ideas. We went to Da Lat and enjoyed our time there.

6. I like flowers because they are colorful.

• Explanation: "because" is used to explain the reason for something. The speaker likes flowers because they are colorful.

7. You can read a book if you have nothing to do.

• Explanation: "if" is used to introduce a condition. If you have nothing to do, you can read a book.

8. He kept on working until he felt very tired.

• Explanation: "until" is used to indicate a time limit. He continued working until he became very tired.

9. Ravi listens to music while doing his working.

• Explanation: "while" is used to show that two actions are happening at the same time. Ravi listens to music while he is working.

10. You cannot succeed unless you work hard.

• Explanation: "unless" is used to express a condition, meaning that something must happen in order for something else to happen. You cannot succeed if you don't work hard.