Though ______, many laws of nature exist.
| A．not having been discovered | B．having not been discovered |
| C．not having discovered | D．having not discovered |
As is reported, it is 115 years______Peking University was founded.
| A．when | B．before | C．after | D．since |
_____ its role in social education, the Palace Museum is quitting its admission fee for special groups on certain
dates.
| A．Fulfill | B．Having fulfilled |
| C．To fulfill | D．Fulfilled |
--- How messy it is! Kevin, can I come in?
--- Oh, I'm so sorry. The house____.
| A．is being cleaned | B．has been cleaned |
| C．is cleaning | D．was cleaned |
What _ day! My car broke down on the high way and I was late for_____ work.
| A．a; the | B．a; / | C．the; / | D．the; the |
Without your help, I _____such a breakthrough in this project.
| A．hadn't made | B．didn't make |
| C．won't have made | D．wouldn't have made |