Question

Identify the following group of words as an incomplete or complete sentence. If the sentence is incomplete, identify the reason.

They spoke before lunch
incomplete sentence: subordinate clause

complete sentence
incomplete sentence: no subject
incomplete sentence: no verb

which would be the best answer?

Answer 1

This is a complete thought.  It has a subject (They) and a verb (Spoke).

Answer 2

Answer: This is a complete thought.  It has a subject (They) and a verb (Spoke).

Explanation: