According to Einstein's Equivalence Principle, Which of the Following Cannot

Multiple Choice

According to Einstein's equivalence principle, which of the following cannot be distinguished from a system accelerating with uniform acceleration in the presence of no gravity by any measurement within the system?

A) a system moving with constant velocity in the presence of no gravitational force
B) a system that only contains massless objects
C) a system that is not accelerating, but is subject to a uniform gravitational acceleration
D) a system that is moving at the speed of light
E) a system in free fall