________ 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 |
I don’t believe we’ve met before，________I must say you do look familiar.
(2012·新课标全国，25)
| A．therefore | B．although |
| C．since | D．unless |
It’s not easy to change habits，________ with awareness and selfcontrol，it is possible. (2013·重庆，23)
| A．for | B．or |
| C．but | D．so |
Don’t turn off the computer before closing all programs，________ you could have problems. (2013·北京，22)
| A．or | B．and |
| C．but | D．so |
I was glad to meet Jenny again，________ I didn’t want to spend all day with her.
(2013·大纲全国，23)
| A．but | B．and |
| C．so | D．or |
She says that she’ll have to close the shop ________ business improves.(2013·江西，28)
| A．if | B．unless |
| C．after | D．when |