Which of the following sentences would be most appropriate in a speech given to an academic audience?

A. Hey everyone. I guess I need to start this speech about global warming. Do you have any questions before I begin?
B. My speech is about penguins. They are the coolest animals of all time and I love them. Sometimes they are used as comedic characters in movies or tv shows.
C. This speech is going to be about giraffes. Did you know that a giraffe's neck is too short to reach the ground? I've got other trivia facts for you.
D. One of Coke's most famous commercials includes polar bears. Unfortunately, those animals are in danger due to global warming. However, there are some simple and lasting things society can do to help.