根据句义完成句中已给出首字母的单词。

1．Please keep your v________ down，the baby is sleeping now

2．My brother is not old enough to d________ a car．

3．P________ my teacher will come，but I'm not sure．

4．Please speak c________，or I can't understand you．

5．The doctor asked Mr. Wang to give up s________，because it’s bad for his health．