21. Complete the sentence using pronouns: … are going to sell their car.

It's 7:30 pm at Lisa's house and she's in her room doing her homework."My parents keep telling me off for multi-tasking while studying,but they don't understand that it helps me concentrate"-she says. Young people today spend nearly 6 1/2 hours a day using various types of media, doing different things at the same time. ''Multi-tasking affects how you learn in a negative way,'' says Russell Poldrack , Associate Professor of Psychology at UCLA. It is as if they're afraid of silence,'' says Casey Roberts, a secondary school teacher. ''Their MP3 players, laptops and games consoles have become extensions of themselves.