Professor Li always allows his students to voice their opinions in class, ______ sometimes their opinions are not sound.
| A．so that | B．in case | C．even if | D．as though |
_______ many times, he finally understood it．
| A．Taught | B．Teaching | C．Having taught | D．Having been taught |
Ladies and gentlemen, please remain ________ until the plane has come to a complete stop．
| A．seated | B．seating | C．to seat | D．seat |
He told us whether _________ a picnic was still under discussion．
| A．to have | B．having | C．have | D．had |
--Has your teacher returned from America yet?
--Yes, but he _______ here for only three days before his company sent him to Africa．
| A．was | B．has been | C．will be | D．would be |
It is said that he will______ his uncle’s business when he is mature enough to deal with the pubic relations．
| A．think over | B．hand over | C．take over | D．go over |