The flu is believed ______ by viruses that like to reproduce in the cells inside the human nose and throat.
| A．to be caused | B．to have caused | C．being caused | D．causing |
__________ she couldn't understand was__________ fewer and fewer students showed interest in her lessons.
| A．What; why | B．That; what | C．What; because | D．That; why |
Scientists say it may be five or ten years___________ it is possible to test this medicine on human patients.
| A．since | B．before | C．after | D．when |
The girl__________ on the ground __________to me that she had___________ the book on the shelf.
| A．lying; lay; laid | B．lay; lied; laid |
| C．lie; lied; lay | D．lying; lied; laid |
--Did Mary come to your birthday party?
--No. I __________ her, but she was away on business.
| A．would like to invite | B．would have liked to invite |
| C．must have invited | D．could invite |
All the preparations_____, we're ready to start.
| A．made | B．being made | C．having made | D．have been made |