15. When Madam Curie did the experiment again, she was more careful where she _____ a mistake.
| A．made | B．has made | C．was making | D．had made |
He apologized for ______ to inform me of the change in the plan.
| A．his being not able | B．him not to be able |
| C．his not being able | D．him to be not able |
more time, we could do it better.
| A．Giving | B．Given | C．Give | D．To give |
Helen plays the violin ________, if not better than, Kate.
| A．as well | B．so well | C．as well as | D．so well as |
—You seem to have known Dr. Ken for a long time.
—That’s true. ________ he joined our club years ago.
| A．Since | B．Until | C．When | D．If |
You _______ her in her office last Friday; she’s been out of town for two weeks.
| A．needn’t have seen | B．must have seen | C．shouldn’t have seen | D．can’t have seen |