1.you can only pass this exam by studying hard
Only by learning hard can you pass the exam
2.you can only understand it when you grow up
Only when you grow up can you understand.
3.I can only realized that I'd seen it before after the film started
Only after the film started did I realize that I had seen it before.
4. the exercise is so easy that every students can do it easily
So easy is the exercise that every students can do it easily.
5.he not only studies well , but also he sings well
Not only does he study well, but also he sings well.
6.If you meet her , please call me
Should you meet her, please ask her to call me at once.
7. If you had obeyed orders this diaster would not have happend
Had you obeyed orders, this disaster would not have happened.