请教all of与of all的用法区别

william_T

12.Noise in a room may be reduced by carpeting, draperies and upholstered furniture, _____absorb sound.

(A) which they all

(B) of them all

(C) all of which

(D) of all which

答案是C没有异议。但我一直没有真正弄清all of与of all在用法上的区别，所以还请各位大大帮我讲讲清楚，谢谢啦！

drift_er

all of +限定词＋名词；

of all 可以直接加名词；

which之前用all of