－I knocked at your door, but nobody answered．

－You should ________ the door bell．

try touching

tried to touch

have tried touching

have tried to touch

－You haven’t got the textbook for my chemistry course yet．

－I know, and we ________ to get it for the last five weeks．

will have been trying

have been trying

will be trying

have tried

－I’m tired, Father?

－Tired?________?

For what

Of what

In what

By what

It ________ 2 years since we began to use the machine．

was

have been

had been

is

He thought it was time for the man got rid of ________ his plan．

to carry out

carrying out

carry out

carry out

She ________ a secretary for 5 years, but now she is a manager of a big store．

is

was

had been

has been

－This return Chinese scholar has become one of the top experts in this field．

－Yes, I know him very well．He ________ in Africa with animals for 8 years．

has worked

had worked

worked

has been working

Although medical science ________ control over several dangerous diseases, ________ worries us is ________ some of them are returning．

achieved; what; that

has achieved; what; that

will achieved; that; why

had achieved; what; how

The fact ________ he didn’t recognize me means that I ________ a lot in the past few years．

that; changed

which; had changed

when; changed

that; have changed

－I suppose Jack is late again．

－You ________ it!

are guessing

will guess

guess

have guessed