Dear Students,
Study the following rules to help you in tenses:
1- Have or has + P.P +Since +Past simple
I haven't met my best friend since she went to London.

2-After + past perfect + past simple

After I had done my h.w.I watched T.V.

3- Before + past simple + past perfect

Before she arrived,I had cooked lunch.

4-While /As/Just as +past continuous + past simple

While I was studying my lessons,the light went out.

5-When + past simple +past continuous

When she came the children were doing their h.w.