Not only Tom but I and Bob ________ a lot of English songs so far．

has learned

have learned

learned

had learned

Don’t come tomorrow．I’d rather you ________ next weekend．

must

should

would

came

When first ________ to the market, these products enjoyed great success．

introducing

introduced

introduce

being introduced

Even if ________, I won’t go to such a bad lecture．

being invited to

invited to

was invited to

having been invited to

________ he makes up his mind, Sam will never give up．

While

Though

As soon as

Once

The research is so designed that once ________ nothing can be done to change it．

begins

having begun

beginning

begun

Camels can ________ in desert for many days without water．

survive

exist

suffer

last

As a result of destroying the forests, a large ________ of desert ________ covered the land．

number; has

quantity; has

number; have

quantity; have

As far as traffic is concerned, no city can compare ________ New York．

to

for

in

with

If you compare her work ________ his, you’ll find hers is much better．

at

in

with

by