______ it have been the failure to pick up directions from the ground control that caused the air crash?
| A．Must | B．Could | C．Would | D．Should |
___________Mrs Smith worked day and night, he found it difficult to make enough money to support such a large family.
| A．Since | B．If | C．Once | D．Although |
___________ with the size of the whole earth, the biggest ocean does not seem big at all.
| A．Compare | B．Comparing | C．When compared | D．When comparing |
The number of private cars in urban areas should be limited ___________the number of public buses should be increased.
| A．when | B．while | C．unless | D．until |
the teacher us, we can make great progress.
| A．With; to lead | B．With; lead | C．As; lead | D．As; leading |
The young man tried to live by writing, but it didn’t provide a good enough ___________.
| A．money | B．value | C．bill | D．income |