The two boys look so much alike _______no one can tell them apart.
| A．so that | B．that | C．and | D．as |
It is difficult for us to learn a lesson in life______we’ve actually had that lesson.
| A．until |
| B．after |
| C．since |
| D．when |
“You can’t have this football back_____you promise not to kick it at my cat again.” the old man said firmly.
| A．because |
| B．since |
| C．when |
| D．until |
environmental damage is done, it takes many years for the ecosystem（生态系统）to recover.
| A．Even if |
| B．If only |
| C．While |
| D．Once |
____, he talks a lot about his favorite singers after class.
| A．A quiet student as he may be |
| B．Quiet student as he may be |
| C．Be a quiet student as he may |
| D．Quiet as he may be a student |
You must keep on working in the evening, you are sure you can finish the task in time.
| A．as |
| B．if |
| C．when |
| D．unless |