When and why he came here ________ yet.
| A．is not known | B．are not known | C．has not known | D．have not bee |
A lot of language learning ,_______has been discovered, is happening in the first year of life, so parents should talk much to their children during that period .
| A．as | B．it | C．which | D．this |
That Jill was worried seemed _____ to everyone present at the meeting.
| A．constant | B．evident | C．previous | D．rough |
Having finished her project ,she was invited by the school______ to the new students.
| A．speaking | B．having spoken | C．to speak | D．to have spoken |
The calculations, had they been done by hand, ______all practical value by the time they were finished.
| A．had lost | B．would lose | C．should have lost | D．would have lost |
After school we went to the reading-room to do some reading ,only to be told that it _______.
| A．was decorated | B．had decorated |
| C．had been decorating | D．was being decorated |