从警察起源上看，( )。

A．警察是一个历史范畴
B．原始社会也有警察
C．警察是先于国家的产生而产生的
D．警察永世长存

It is very kind _____ you to help me with my lessons because it is very difficult _____me to learn them well.

A．of； for

B．of； of

C．for；of

D．for； for