Question

Read the following sentence:

At the robotics convention, the engineers did speak with multiple consumers about product improvement.

What is the purpose of the auxillary verb, did, in this sentence?

A.
It is an action verb not an auxillary verb.
B.
It describes the subject of the sentence.
C.
It acts like an adverb of the action verb, speak.
D.
It reinforces the action verb, speak, and the degree of certainty that the action occurred.