Ответ:
Task 1.
1. While I was searching for my keys, I found the note.
2. Helen and Rob were watching TV when they heard a loud scream.
3. While we were going to into town, Max began to feel ill.
4. The volcano erupted as people were climbing it.
5. Dan asked teacher for help while he was doing the maths.
Task 2.
1. when
2. walked
3. were waiting
4. were talking
5. started
Task 3.
1. imagination
2. preparation
3. relax
4. employees
5. accomplishment
Task 4.
1. It's a stunning part of the country.
2. My uncle lives on a tiny island in the Pacific.
3. That new school band is awful.
4. ..., and now my clothes is filthy.
5. ..., it's always delicious.