Решение:
- I can't help you unless you tell me what's wrong.
- My mum was really exhausted. She looked as if she was about to pass out.
- I learned how to swim when I was a little girl.
- The water of the lake was deep, for clear.
- She missed the train after her door lock broke down.
- The party will start at 11.30 yet the presentation finishes.
Ответ: unless, as if, when, for, after, yet.