用所给词组的适当形式填空。

be able to     hear of     keep…down    fall in love     pick up

Have you ever __________ __________ Donald Duck?
She’s doing her homework. Would you mind _________ your voice_________?
We often see the boy __________ __________ the litter in the school yard.
He _________ __________ __________ drive a car when he was 18.
Last summer Lisa went to Guilin. She __________ __________ __________ with it.