Tenses Revision

The screen of a PC__________ a good user interface.

• is providing

• provides

• provide

The files _______since my last backup.

• had changed

• have changed

• changed

There was a power cut while I______ my computer.

• was using

• used

• had used

Before IBM set the standard for PCs, software houses_____ different versions of their programs for every make of computer.

• have written

• had wrote

• had written

When I came, they____ the question for more than an hour.

• were discussing

• had been discussing

• had discussed

I ___ how this robot works.

• am not understanding

• don't understand

• doesn't understand

Right now we_____ the rate of technical progress every decade.

• double

• have been doubling

• are doubling

I _____ a pre-paid charge card for small purchases. Now I can buy things on the Internet.

• had bought

• have bought

• bought

_____ you____ your site on a search engine yet?

• did... register

• have ... registered

• do ... register

When ____ you ___ communication?

• have ... studied

• did ... study

• did ... studied