Only when I lost the opportunity to take my first job ____ how important it was to me.
A. I realized   B. I had realized    C, had I realized   D . did I realize

Only when the war was over         return home.

The door opened and in        we had never seen before.

Not until the next morning _____ how serious the situation was．

If       carefully, the experiment will be successful.

_________ did the students realize that they were mistaken about spiders.

Don’t be too rude to your father. Never in his life _____ in that way.

So ________ student ________ that he can work out all difficult problems.

__________ can you expect success.

-----Peter likes playing football, but he can’t play it well.
------_____________________.