Question

Select the correct and entire main clause of the sentence.

Have you seen my textbook, Rafael?
The main clause is _____.

Answer 1

The entire sentence is the main clause. The part that might confuse you is the comma separating "Rafael" but that only means that it's a vocative case. 

Answer 2

The correct answer is: Have you seen my text book?

The correct main clause of the sentence is Have you seen my text book?

This sentence is a complete one. It is understood as it is. The sentence is clear. It has a subject and predicated. There is no need for other words or expressions in order to understand it. A main clause can form a full sentence or a complete sentence by itself. If a coma appears in the sentence, it is still a main clause.