knock knock! (THIS IS A JOKE THO)

This joke blog needs a knock-knock joke. i'll be the first. thank you.

A: knock knock,
B: who's there?
A: BOO
B: BOO who?
A: ooh. pls dun cry i didnt mean to scare u.

A: knock knock
B: who's there?
A: president
B: president who?
A: president Hu(who) Jin Tao!