3.It started raining last Friday and has not stopped yet.
→It has been raining since last Friday
4.The last time I played tennis was in 1990.
→I haven’t played tennis since1990
5.The children went to bed. We watched TV.
.→After the children had gone to bed,we watched TV

1) I haven’t been to the dentist for two year.
=> It is 2 years since I last went to the dentist.
2) This is the first time I have driven a car.
=> I have never driven a car before.
3) It started raining last Friday and has not stopped yet.
=> It has rainend since last Friday.
4) The last time I played tennis was in 1990.
=> I haven’t played tennis since 1990
5) The children went to bed. We watched TV.
=> After the children went to bed, we had watched TV.
6) How long is it since you started learning English?
=> When did you start learning English?
7) Originally, tennis was an indoor game.
=> Tennis used to be an indoor game.
8) He found a job in a steel mill, and then he got married.
=> After he found a job in a steel mill, he had got married.
9) It is ten years since I last met David.
=> I haven’t met David for ten years.

1) I haven’t been to the dentist for two years.
----> It is two years since I went to the dentist.

2) This is the first time I have driven a car.
----> I have never driven a car before.

3) It started raining last Friday and has not stopped yet.
------> It has been raining since last Friday. 

4) The last time I played tennis was in 1990.
-----> I haven’t played tennis since 1990.

5) The children went to bed. We watched TV.
-----> After the children went to bed,we had watched TV.

6) How long is it since you started learning English?
----> When have you started learning English ?

7) Originally, tennis was an indoor game.
----> Tennis used to be an indoor game.

8) He found a job in a steel mill, and then he got married.
---> After he found a job in a steel mill,he had got married.

9) It is ten years since I last met David.
----> I haven’t met David for ten years.

How long have Mary and John been married ? =>  When.....................