______some people are motivated by a need for success, others are motivated by a fear of failure.
| A． |
Because |
B． |
If |
C． |
Unless |
D． |
While |
You have to wear a helmet and a life jacket for protection, just ___ you fall into the water.
A. in case C. unless
C. though D. As
I toured the Great Wall，I was deeply impressed with the beautiful scenery．
| A．For the first time | B．At first |
| C．The first time | D．It was the first time |
He was about to leave the office for home _______someone knocked the door and asked for some help.
| A．until | B．while |
| C．as | D．when |
If you find yourself ______ no one will help you, please call me.
| A．which | B．when |
| C．where | D．what |
The government has taken some measures to solve the shortage of water, but it may be some time __ the situation improves.
| A．since | B．when. |
| C．unless. | D．before. |