1£®She has two daughters. One of them is a doctor.

She has two daughters, one of whom is a doctor.

2£®The boy was often late for school. The reason is still unknown.

The reason for which/why the boy was often late for school is still unknown.

3£®China has thousands of islands. Hainan Island is the largest among them.

China has thousands of islands, of which Hainan Island is the largest.

4£®Recently I bought an ancient Chinese vase. Its price was very reasonable.

Recently I bought an ancient Chinese vase, the price of which was very reasonable.

5£®In the distance there is a hill. On the top of it stands a white temple.

In the distance there is a hill, on the top of which stands a white temple.

6£®I have bought two books recently. Neither of them interests my brother.

I have bought two books recently, neither of which interests my brother.