George would certainly have attended the meetings, _____.
| A．has he not had a flat tyre |
| B．if he hadn’t a flat tyre |
| C．had he not had a flat tyre |
| D．if he hasn’t had a flat tyre |
．Children are not recommended to see such films___________bad for their mental development.
| A．that is | B．that are | C．as are | D．as is |
Because of Einstein’s Theory of Relativity, scientists never again regarded the world___________.
| A．as before they did | B．as they regarded before |
| C．as they did before | D．as they had before |
--- Hurry up. The bus is coming.
--- Oh, no. We mustn’t cross the street___________the traffic lights are green.
| A．until | B．since | C．while | D．after |
Sorry, you lost your purse; I hope it will___________some day.
| A．turn out | B．show off | C．show up | D．turn up |
A brilliant idea occurred to him, ___________to his research in the lab.
| A．while devoting | B．while devoting himself |
| C．while he was devoted | D．while devoted |