He failed the mid-term examination and only then _______ how much time he had wasted.
| A．had he realized | B．did he realize |
| C．he had realized | D．he realized |
In order to go to a key university, I must______my study from now on.
| A．consist of | B．get away from | C．concentrate on | D．come up with |
The English teacherher students how to improve their comprehension skill since last week.
| A．has told | B．is telling | C．has been telling | D．will have told |
---- Sorry, I have to ______ now. It’s time for class.
---- OK, I’ll call back later.
| A．hang up | B．break up | C．give up | D．hold up |
Before a problem can be solved, it must be obvious ______the problem itself is.
| A．what | B．that | C．which | D．why |
In the global economy, a new drug for cancer, it is discovered, will create many economic possibilities around the world.
| A．whatever | B．whoever | C．wherever | D．whichever |