ever since while as soon as  since before until however
I'll leave __________ I'm ready.
One can't see air；__________，it does exist.
The telephone rang __________ I was in the garden.
__________ we came to the university, we have learnt quite a lot，
I've never got any letter from him __________ he left.
Only two days remained __________ the examination.
He worked in Hong Kong __________ his father found a job for him in Canada.