________ several times，but he still doesn't know how to do it correctly.
| A．Although I've taught him |
| B．I've taught him |
| C．Having been taught |
| D．Having taught |
The _____ in temperature is broadcast twice a day in the channel.
| A．diversion | B．variety | C．variation | D．diversity |
Such a good opportunity, once ______, might never come again.
| A．lost | B．to lose | C．losing | D．loses |
_________ you may have, you should gather your courage to face the challenge.
| A．Whatever serious a problem | B．However serious a problem |
| C．However a serious problem | D．No matter how a serious problem |
Faced with difficulties, you should believe your confidence is _______ makes a difference.
| A．what | B．that | C．which | D．whether |
Reality is not the way you wish things to be,______ the way they actually are.
| A．as | B．or | C．but | D．and |