1.
Quote:
Quote thadajirajaras  1) Hello teacher--> Can I put the subject "I" in front of "Hello"? |
Hello is not a verb but an interjection. Only verbs have subjects.
2)
Quote:
Quote thadajirajaras Good morning teacher--> Why is there no verb? |
The same explanation - because
Good morning is another interjection made up of a noun phrase (adjective+noun). If you like, you can think of it as meaning :
I wish you a good morning. We would be very unlikely to actually say that however.
PS. Remember what I said in a previous post about the use of the word "teacher" being inappropriate in English as a form of address.