what only if

what if:如果...将会怎么样
例如:
1.What if it is true?
如果这是真的又该如何呢?
2.What if he doesn't agree?
如果他不同意该怎么办呢?
3.What if he comes back now?
如果他现在回来怎么办?
4.What if I fail!
即使我失败了又怎样!
5.What if the boy's parents should die?
如果那男孩的父母死了该怎么办呢?
only if:conj.只有当(只是在...的时候)
例如:
1.The company will succeed only if it have sufficient backing.
只有当该公司获得足够的资助,它才会成功.
2.A compound proposition that has components joined by the word and or its symbol and is true only if both or all the components are true.
综合命题由和或其符号所连接的子句组成的复合命题,只有当所有子句为真时,该句才为真
3.I can buy the house only if a mortgage for 2000 dollars is available.
只有拿到两千美元的抵押贷款,我才买得起那栋房子.
4.Only if I get a job will I have enough money to go to school.
我只有找到了工作才有足够的钱上学.