______ life began on earth is one of the biggest puzzles that scientist found hard ______.
| A．How; solving | B．When; to be solved |
| C．How; to solve | D．Which; to solve |
I’ve tried very hard to improve my English. But by no means with my progress______.
| A．the teacher is not satisfied | B．is the teacher not satisfied |
| C．the teacher is satisfied | D．is the teacher satisfied |
At the foot of the mountain______.
| A．a village lie | B．lies a village | C．does a village lie | D．lying a village |
The hurricane damaged many houses and business buildings；______，it caused 20 deaths.
| A．or else | B．therefore | C．after aU | D．besides |
__________ fired, your health care and other benefits will not be immediately cut off.
| A．Would you be | B．Should you be | C．Could you be | D．Might you be |
So difficult____it to work out the problem that I decided to ask Tom for advice.
| A．I did find | B．did I find | C．I have found | D．have I found |