Final answer:
The curvature of an open universe resembles a saddle shape.
Step-by-step explanation:
In terms of curvature, an open universe resembles a saddle shape (option B). An open universe is negatively curved, which means that you can travel an unlimited distance in any direction.
On the other hand, a flat universe (option A) would have zero curvature, and a closed universe (option C) would have positive curvature, similar to the surface of a sphere.