`a,`

1. They enjoy staying on a farm during their summer vacation

2. We will live a happier and healthier life if we keep our environment clean

3. We shouldn't throw rubbish on the street

4. The students of our school often collect waste paper for their mini project

5. My aunt has a small garden and she grows flowers and vegetables (in the garden)

`b,`

1. They plan to make this beach a clean and beautiful place again

2. The students have collected old clothes for their charity programme since last week

3. If we use the car all the time, we will make the air dirty

4. Unless I leave now, I will miss my train

5. If I don't have a quiet room, I won't be able to do anything

`c,`

1.  We can't use water in this well because it's not really good

2. It's quiet and peaceful in the country, so many people want to live there

3. Unless you study hard, you won't pass the exam

4. Using public transport is a good way to reduce emissions 

5. We'll have to go without John if he doesn't come