7.Although the causes of cancer ____， we do not yet have any practical way to prevent it.
| A．are being uncovered | B．have been uncovering |
| C．are uncovering | D．have uncovered |
—Your sister nearly _____ all her spare time to her study during the three years.
—That's right, or she _____ the first place in her school in the College Entrance Examination.
| A．spent; wouldn't have taken | B．devoted; wouldn't have taken |
| C．hadn't devoted; hadn't taken | D．hadn't spent; couldn't |
He always works hard, but__________, he didn't pass the exam.
| A．much to our surprise | B．to our great surprising | C．to our surprise much | D．to surprise |
The book_______well.
| A．is sold | B．has been sold | C．selled | D．sells |
On _______ side of the river there are a lot of trees.
| A．both | B．any | C．either | D．neither |
At last she made herself ______ by drawing a picture.
| A．understand | B．to understand | C．understood | D．understanding |