15．______ is often the case, we have worked out the production plan.

A．Which　 　　　　　　　　 B．When　 　　　　　　　　 C．What　 　　　　　　　　 D．AS

14．The flu is believed _____by viruses that like to reproduce in the cells inside the human nose and throat.

　　　　 A．causing　 　　　　　　　　 B．being caused　 　　 C．to be caused　 　　　 D．to have caused

13．-How did you find the talk this morning?　

　　　　 -______.

　　　　 A．By asking my students　　　　　　　　　　　　　　　　　 B．It was easy to find

　　　　 C．Very disappointing　　　　　　　　　　　　　　　　　　　　　 D．Just in time for it

12．The flowers _________sweet in the botanic garden attract the visitors to the beauty of nature．

　　　　 A．to smell　　 　　　　 B．smelling　　　 　　 C．smelt　　　 　　　　　 D．to be smelt

11．--You have made progress in your English study, haven’t you?

--Yes, but much ____.

A remains to do　　 B is remained to do

C remains to be done D is remained to be done