_____the cause of the oil leaks, the specialists can not draw a conclusion before completing a thorough and detailed investigation.
| A．With regard to | B．Regardless of |
| C．In response to | D．In spite of |
Please call my secretary to arrange a meeting this afternoon，or________it is convenient to you.
| A．whenever |
| B．however |
| C．whichever |
| D．wherever |
He was so deep in thought，thinking of the problem ________ he knocked into the tree without noticing it.
| A．when |
| B．while |
| C．because |
| D．that |
________you’ve experienced it，you can’t understand how I felt.
| A．Once |
| B．Because |
| C．Unless |
| D．While |
________ you may have，you should gather your courage to face the challenge.
| A．However a serious problem |
| B．What a serious problem |
| C．However serious a problem |
| D．What serious a problem |
Paul was not allowed to work he was fully recovered from the flu.
| A．even if |
| B．whether |
| C．because |
| D．until |