—Is there any vaccine(疫苗) against H1N1 flu that can be used on humans?
—No, but scientists are working to develop ________ .
A.that | B.it | C.one | D.so |
23. Everyone should remember it is very important to _____ the balance of nature toady.
A.get | B.make | C.keep | D.Remain |
22. She always ____ her opinion ____ facts.
A.depends, on | B.bases, on | C.put, into | D.bases, by |
21. Every morning, the fish mongers stood there ______ with the fishermen for fishes.
A.to argue | B.to talk about prices | C.bargaining | D.Discussing |
20. When Jack arrived, he learned Mary ____ for almost an hour.
A.had gone | B.had set off | C.had left | D.had been away |
19. They didn't _____ the wedding because of a heavy rain.
A.join | B.take part | C.attend | D.Appear |