We need to get to the root of the problem______ we can solve it.
A. while B. after
C. before D. as
If you miss this chance, it may be years ____ you get another one.
A. as B. before
C. since D. after
_____the damage is done, it will take many years for the farmland to recover.
A. Until B. Unless
C. Once D. Although
He is a shy man,___he is not afraid of anything or anyone.
A. so B. but
C. or D. as
_______online shopping has changed our life , not all of its effects have been positive.
A. Since B. After
C. While D. Unless
The children, ______ had played the whole day long, were worn out.
A. all of what B. all of which
C. all of them D. all of whom