What Was Einstein's Main Reason for Proposing the Principle of the Constancy

Multiple Choice

What was Einstein's main reason for proposing the principle of the constancy of lightspeed?

A) The Michelson- Morley experiment showed that every observer observes the same speed for any lightbeam.
B) He believed that conservation of energy should be obeyed in every nonaccelerated reference frame.
C) His own observations of such simple phenomena as reflection and refraction convinced him that light must have the same speed for all observers.
D) This principle followed from his conclusions regarding the relativity of time and space.
E) He believed that Maxwell's theory of electromagnetism should obey the principle of relativity.