____ that silver is not widely used as a conductor?
| A．Why is | B．Is it why | C．Why is it | D．Why is that |
The teacher stressed again that the students should not ________ any important details while retelling the story.
| A．figure out | B．let out | C．leave out | D．pick out |
—The guard keeps watch at the gate.
—So he does. Only those knows well could be let in.
| A．close; who | B．tight; whom | C．tight; that | D．close; he |
He _______ have escaped, but he chose to stay and fight.
| A．must | B．could | C．will | D．need |
_______, according to the instructions, the medicine, I think, will work on your headache before long.
| A．Take | B．Being taking | C．Taken | D．Taking |
Only after spending several nights working on the math problem to wonder whether the problem was wrongly set.
| A．had he begun | B．he began | C．did he begin | D．began he |