1. It's very important to keep the environment.

2. I haven't spoken to her for three years.

1. When did you begin using the car ?

5. We have lived here for 15 years.

6. The water isn't cold enough to drink.

7. It started to rain five hours ago.

8. It is a good activity to help mom at home.

1) Keeping the environment clean is very important. 

⇒ It’s very important to keep the environment clean.

2) It’s three years since I last spoke to her.

⇒ I haven’t spoken to her for three years.

3) How long is it since you used the car?

⇒ When did you begin to use the car?

4) We started living here 15 years ago.

⇒ We have lived here for 15 years.

5) We can’t drink the water because it’s too hot.

⇒ The water isn’t cold enough for us to drink the water.

6) It has been raining for five hours.

⇒ It started raining five hours ago.

7) To help mom at home is a good activity.

⇒ It is good to help mom at home.