1. They bought this house ten years ago.

→ They have bought this house for ten years. 

2. Jane gave me a present on my last birthday.

→ I was given a present on my last birthday

3. I last saw Bob when I was in Ho Chi Minh City.

→ I haven't seen..... Bob since I was in HCM city. 

4. It is a three-hour drive from Hanoi to Nam Dinh. → It takes.........three hours to drive from HN to ND

5. The children couldn't go swimming because the sea was very rough.

→ The sea was too......tough for the children to go swimming 

6. All the students love the principal because he is very kind.

→ Owing to the principal's kindness, all the students love him