After David had gone home we arrived.

We had lunch then before took a look around the shops. 

The light had gone out when we got out of the office. – When 

 she had explained everything clearly by the time we started our work. – By the time 

1. After we arrived, David had gone home.

2. Before we took a look around the shops, we had lunch.

3. When we got out of the office, the light had gone out.

1. After David had gone home, we arrived.

2. Before we had lunch , we took a look around the shops.

3. When we got out of the office, the light had gone out,

4. By the time we started our work, she had explained everything dearly