Only when I 
left my parents for America ____ how much I loved them.
| A．I realized | B．I had realized | C．had I realized | D．did I realize |
I really appreciate some time to surf the Internet. But I am too busy.
| A．to have | B．to having | C．have | D．having |
I failed in the final exam last tem. Only then the importance of studies.
| A．I realized | B．I had realized | C．had I realized | D．did I realized |
A great fire in our town last night and many people became homeless.
| A．broke through | B．broke off | C．broke out | D．broke down |
The country’s car industry is so strongly protected that foreign cars are seen there.
| A．immediately | B．rarely | C．correctly | D．similarly |
.By the time the tornado ended, more than 700 people _________.
| A．have killed | B．had been killed | C．were killed | D．had killed |