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If如果, unless除非, as long as只要, As (so) far as --- 据……所知，in case万一, provided that假如, on condition that若是，以…为条件
If you don’t hurry up, you will miss the plane.
Unless --- 如果不, 除非=if notWe can’t get there on time unless we book the earliest flight
We will succeed as long as we keep on trying.
As far as I know, he speaks English very well.
The plane cannot take off in case it rains.
Provided that 如果,有时省略 thatThe plane will be in good condition provided that it is taken care of carefully.
On condition that --- 条件是…He said that he would come to the meeting on condition that no one asked him to speak.
注:主从句的动作发生在将来时，则主句用将来时, 从句用一般现在时。If he arrives tomorrow, I will be waiting for him at the airport.
