1. I have a friend. Her mum is a volunteer worker.

`->` I have a friend whose mum is a volunteer worker.

2. It is a camping shop. It has a lot of good equipment.

`->` It is a camping shop which has a lot of good equipments.

3. The rescue operation was arranged by a charity organization. It was a success.

`->` The rescue operation which was arranged by a charity organization was successful.

`=>` Dùng which cho rescue operation để nối lại câu

4. My uncle is a firefighter. He visited us last weekend.

`->` My uncle visited us last weekend who is a firefighter.

`=>` Vì có is nên dùng who.

5. 2015 is the year. My sister became a nurse.

`->` My sister became a nurse in 2015

6. The storm started at 2 o’clock this morning. It caused a lot of damage.

`->` The storm which caused a lot of damage started at 2 o’clock this morning.

`=>` Để chỉ cơn bão thì dùng which.

7. Nick is my classmate. I’ve known him for a long time.

`->` I've known Nick for a long time who is my classmate.

`=>` Có to be is nên dùng who phía trước.