Question

select the words that make up the complete subject. a mechanical problem with the plane caused a delay in our departure time.

Explanation:

The complete subject of a sentence includes the simple subject (the main noun or pronoun) and all the words that modify it. In the sentence "A mechanical problem with the plane caused a delay in our departure time", the simple subject is "problem", and the words modifying it (including the article, adjective, and prepositional phrase) are "A mechanical problem with the plane".

Answer:

A mechanical problem with the plane