－Where did you put the car keys?

－Oh．I ________ I put them on the chair because the phone rang as I ________ in．

A．remembered; come

B．remembered; was coming

C．remember; come

D．remember; was coming

As you can see, the number of cars on our roads ________ rising these days．

A．was keeping

B．keep

C．keeps

D．were keeping

The water ________ cool when I jumped into the pool for morning exercise．

A．was felt

B．is felt

C．felt

D．feels

Although the causes of cancer ________, we do not yet have any practical way to prevent it．

A．are being uncovered

B．have been uncovered

C．are uncovering

D．have uncovered

The moment the 28th Olympic Games ________ open, the whole world cheered．

A．declared

B．have been declared

C．have declared

D．were declared

Customers are asked to make sure that they ________ the right change before leaving the shop．

A．will give

B．have been given

C．have given

D．will be given

Now that she is out of a job, Lucy ________ going back to school, but she hasn't decided yet．

A．had considered

B．has been considering

C．considered

D．is going to consider

By the time Jane gets home, her aunt ________ for London to attend a meeting．

A．will leave

B．leaves

C．will have left

D．left

The crazy fans ________ patiently for two hours, and they would wait till the movie star arrived．

A．were waiting

B．had been waiting

C．had waited

D．would wait

I won't tell the student the answer to the math problem until he ________ on it for more than an hour．

A．has been working

B．will have worked

C．will have been working

D．had worked