Which of the following best describes the "object model" used when analyzing motion in introductory mechanics?
a) The real object is represented as a rigid body whose size and shape are fully included, but its internal forces are ignored.
b) The real object is represented as a dimensionless point that possesses no mass, so inertia can be neglected.
c) The real object is represented as a dimensionless point that possesses mass but no spatial extent.
d) The real object is represented as a rigid body whose shape can deform slightly during motion.