As usual，he put on a show as though his trip __________a great success.
| A．had been | B．has been | C．were | D．was |
He lay ___ the grass was the thickest.
| A．where | B．when | C．that | D．after |
Go back ___ you came from.
| A．until | B．where | C．which | D．when |
The doctor will not perform the operation ___ it is absolutely necessary.
| A．when | B．if | C．for | D．unless |
Difficulties are nothing ___ we are not afraid of them.
| A．for | B．as | C．if | D．whether |
―When do we need to pay the balance ?
― September 30.
| A．In | B．By | C．During | D．Within |