Why would you choose subjects like "My Hobby" or "My Pet" for a five minute speech?
A. Topics like exponential notation, semantics, etc. are not usually topics that can be covered in five minutes.
B. I would have little or no knowledge about topics like exponential notation, semantics, etc.
C. Talking about a pet or a hobby can be done in five minutes.
I would say C. A and B could also be selected, but that depends on what you've been taught in class. If you were specifically TAUGHT semantics, or exponential notation, then it could be different.