Normally you are a multi-atomic human existing in three-dimensional space. But your fairy godmother fulfills your deepest wish, and you are magically transformed into a rigid (non vibrating) diatomic molecule living in two-dimensional flatland. In other words, you are made up of two atoms and can only move about in the x-y plane. Your internal energy is

A. undefined
B. 1/2 kT
C. kT
D. 3/2 kT
E. 2kT