His failure made him aware ___ he had made a great mistake in working out the plan.
| A．of that | B．of | C．that | D．that of |
If only you __________ him what I said! Everything would have been all right.
| A．didn't told | B．hadn't told |
| C．would not tell | D．would have not told |
We didn't know his telephone number, otherwise we _________ him.
| A．would have telephoned | B．must have telephoned |
| C．would telephone | D．had telephoned |
It was essential that the application forms ___________ back before the deadline .
| A．must be sent | B．would be sent |
| C．be sent | D．were sent |
_____________ cease（终止） advertising, prices would be significantly reduced.
| A．Were they to | B．Could they |
| C．If they | D．Would they |
Much labor would have been saved if the electronic computers_____________ before.
| A．had invented | B．were invented |
| C．should have been invented | D．had been invented |