When you're introducing a presentation,include a(n) ________ to help your audience understand the structure and content of your message.

A) catalogue of sources
B) preview section
C) bimodal transition
D) contextual pattern
E) executive summary

A preview section is the best choice for introducing a presentation as it gives the audience an overview of what to expect from the presentation. It provides the structure and content of the message to be delivered, and prepares the audience for what is to come. A catalog of sources and an executive summary can be useful in some contexts, but are not as relevant for introducing a presentation. Bimodal transition and contextual pattern are not commonly used terms in the context of presentation introductions.