A formal sentence should include subject, verb and sometimes object.
Any sentence that is short for an element of those is called incomplete sentence.
Who was the 35th president?
I can use the word "have" at the beginning of a sentence if it fits grammatically. Could you please provide a sentence where you would like me to include the word "have"?
Noun or pronoun.
I have an obligation to attend the meeting tomorrow.
Writing an answer to this question is "inconvenient" for me.
I have a special pet in the entire world.Guess what it is?
His devotion to his training set an example for the other students.
The school forbids students from using their phones during class.
We need the police to enforce law and order
I will now taunt you by not answering this question properly.
Convection causes it to rise, causing a valley breeze
Wrong. You must say, "the scissors are on the table"