people are distributed can also affect the education system.
| A．Why | B．How | C．What | D．When |
You will have to wait for one more week, _________ the manager will be back from his trip.
| A．when | B．before | C．as | D．until |
_________ environmental damage is done, it takes many years for the ecosystem to recover.
| A．Even if | B．If only | C．While | D．Once |
After he became conscious, he remembered _________ and _________ on the head with a rod.
| A．to attack; hit | B．to be attacked; to be hit |
| C．attacking; be hit | D．having been attacked; hit |
Human facial expressions differ from those of animals in the degree _________ they can be controlled on purpose.
| A．with which | B．of which | C．to which | D．for which |
David and Susan didn’t give in to each other, so they _________ the whole time they were together.
| A．have quarrelled | B．had quarrelled |
| C．were quarrelling | D．had been quarrelling |