According to the theory of relativity, which of the following always remains constant ?

A. Length of an object
B. Time
C. Space
D. Velocity of light

Explanation:

One of the oddest things about our universe is that it has some fundamental constants. Thus, for his theory of relativity to work, he hypothesized that the speed of light must remain constant. In the century since Einstein developed his theory, every conclusion he made has been proven to be correct.