When noah was building a boat, people thought he was crazy, ignored him, called him names
The answer would be an opportunity cost
The complete verb is A. can't wait.
The complete verb is the main verb and all of the auxilary verbs together.
In this sentence, "cannot" is the helping verb, and "wait" is the main verb. "Cannot wait" is the complete verb phrase.
It depends if you are writing a personal one, a persuasive one, an argumentative one, historical one, etc.