Which of the following is the same in all frames of reference?

A. Length of an object

B. Speed of light

C. Mass of an object

D. Rate of time passage

The correct option is B.

The length of an object, the mass of an object and the rate of time passage for an object can change depending on the situation which the object is subject to. For instance in space, the mass and the velocity of an object usually change. But, the value of the speed of light in the space is the same for all observers regardless of the motion of an object, that is, the speed of light is a constant.