A: it would be a rectangular prism as well! a section perpendicular to the base is parallel to the sides of the prism
B: the section would be a triangular prism!
whenever I get those questions, I always imagine a small cube of cheese, and if you have trouble imagining sections etc, I'd really suggest trying it! it sharpens your mind and helps you understand how it looks! otherwise, a great program for visualizing math problems is geogebra. it not only helps you draw everything out but solves your problems half of the time tbh