They often change the kind of crop in each field ____ few years, for example, growing corn or wheat and then the next year peas or soybeans.
| A．every | B．a | C．each | D．some |
______ is often the case, we have worked out the production plan.
| A．Which | B．When | C．What | D．AS |
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 |
—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 |
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 |
—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