quiet的副词是quietly形容词变为副词的规则：

1. 一般情况下在形容词词尾直接加-ly。如:real-really; helpful-helpfully; careful-carefully; hopeful-hopefully; slow-slowly; quick-quickly; quiet-quietly!

2. 以辅音字母加y结尾的形容词要变y为i,然后再加-ly。如:busy-busily; angry-angrily; easy-easily ；happy---happily

3、某些以辅音字母加不发音的字母e结尾和以-ue结尾的形容词要先去掉e,然后再加-y或-ly。如: terrible-terribly; true-truly; gentle-gently 同学你好，很高兴为你解答。

quiet 是形容词,而形容词一般修饰名词、系动词、感官动词

quietly 是副词 ,副词一般修饰修饰实义动词、形容词

quiet的短语词组

keep quiet  保持安静

in quiet  安定地，平静地  

peace and quiet  安静，宁静

on the quiet  私下地，秘密地

at quiet  平静地，平稳地，安定地