1. While they were cleaning the streets, it started to rain./ They were cleaning the streets when it started to rain.

2. While I was watching TV, I saw the floods and landslides in the area./ I was watching TV when I saw the floods and landslides in the area.

3. While Tim was searching for employment opportunities, he found a job advert from a non-governmental organisation./ Tim was searching for employment opportunities when he found a job advert from a non-governmental organisation.

4. They decided to help build a community centre for young people while they were visiting some poor villages./ When they decided to help build a community centre for young people, they were visiting some poor villages.