By the time he realizes he__ into a trap, it’ll be too late for him to do anything about it.
| A．walks | B．walked | C．has walked | D．had walked |
The Olympic Games ____ held every ____ years.
| A．is;four | B．are;four | C．is;five | D．are;five |
A chemical works____ built there.
| A．is to being | B．have been | C．were to | D．has been |
Chairman Mao' s works ____ published.
| A．has been | B．have been | C．was | D．is |
The Arabian Nights ____ well known to the English.
| A．is | B．are | C．was | D．were |
The number of deer, mountain lions and wild roses ____ much if people leave things as they are.
| A．doesn' t change | B．don't change | C．change | D．changed |