25.After studying chemistry for years, I can only say I have ___ general knowledge of this subject.
| A．/ | B．a little | C．a | D．Some |
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 |
6.I have to go to work by taxi because my car ____at the garage.
| A．will be repaired | B．is repaired |
| C．is being repaired | D．has been repaired |
5.―Have you handed in your schoolwork yet?
―Yes，I have. I guess it ____ now.
| A．has graded | B．is graded | C．is being graded | D．is grading |
4.It is said that the early European playing-cards ____ for entertainment and education.
| A．were being designed | B．have designed |
| C．have been designed | D．were designed |
3.As the years passed， many occasions―birthdays， awards， graduations ____ with Dad’s flowers.
| A．are marked | B．were marked | C．have marked | D．had marked |