Question:

　　Dear Ms ABC,

　　I want to know when we should say "How do you do". What is the difference between "hellow" and "how do you do"?

　　Best regard

　　Xiao cao

　　Answer:

　　Dear Xiao cao,

　　hello和how do you do用法上没有太大的区别，都可以用来打招呼。如果要深究，hello比较随意一些，而how do you do一般用于比较正式的场合，如甲向乙介绍丙，乙就可以说how do you do，而不用hello.

　　Yours abc