What type of channel do Speaker 1 and Speaker 2 use in their communication?

a. visual

b. auditory

c. olfactory

d. tactile

The type of channel that speaker one and speaker two use in their communication would be auditory - b.

The fact that we're talking about "speaker" 1 and "speaker" 2 implies already the fact that both of them are talking and this then implies that they are using the auditory channel of communication.