Each main point of your first speech should:

A. cover a single aspect of the topic.
B. have its own introduction.
C. end with an internal summary.
D. be preceded by a preview statement.
E. begin with a question.

The correct answer is letter D

Explanation: When making a speech there are very important points to be made, both for the audience to be able to follow and understand, as well as to make the audience pay attention and maintain interest in what is said. There are many strategies and ways to keep the audience attentive, one of the most important is to make a preview of the next statement, this will help the understanding of the audience.

permafrost layer, it exists beneath a layer of soil, rock or sediment.