—Bob has gone to California.

—Oh, can you tell me when he ________？

A. has left 

B. left

C. is leaving 

D. would leave

—That must have been a long trip.

—Yeah, it ________ us a whole week to get there.

A. takes 

B. has taken

C. took 

D. was taking

Experiments of this kind ________ in both the U．S. and Europe well before the Second World War.

A. have conducted 

B. have been conducted

C. had conducted 

D. had been conducted

By the time Jack returned home from England, his son ________ from college.  

A．graduated                             

B．has graduated

C．had been graduating                     

D．had graduated

In 1492, Columbus ______ on one of the Bahama Islands, but he mistook it for an island off India.

A．lands                        

B．landed

C．has landed        

D．had landed

Last month,  the Japanese government expressed their thanks for the aid they ________ from China.

A．receive                 

B．are receiving

C．have received           

D．had received

The manager was worried about the press conference his assistant________ in his place but, luckily, everything was going on smoothly.

A. gave                         

B. gives

C. was giving                    

D. had given

She was surprised to find the fridge empty; the children ________ everything!

A. had been eating 

B. had eaten

C. have eaten 

D. have been eating

When I got on the bus, I ________ I had left my wallet at home.

A. was realizing 

B. realized

C. have realized 

D. would realize

When Alice came to life, she did not know how long she ________ there.

A．had been lying

B．has been lying

C．was lying

D．has lain