With the help of high technology, more and more substances _________ in the past years.
| A．discovered | B．have discovered |
| C．had been discovered | D．have been discovered |
The professor can answer almost any question __________we have about any history topic.
| A．as | B．that | C．why | D．where |
Due to the light pollution, stars are too faint _________with naked eyes in the urban area.
| A．observing | B．being observed |
| C．to be observed | D．to be observing |
--Why won’t you go to Jim’s birthday party with us?
--Well, I don’t like him, if you ________know.
| A．can | B．may | C．must | D．should |
He failed the driving test though he __________for a long time.
| A．practises | B．has practised |
| C．was practising | D．had been practising |
Hotels fill up fast during the busy tourist season, __________it is necessary for tourists to make reservations in advance.
| A．or | B．so | C．for | D．but |