In physics, the special relativity (SR, also known as the special theory of relativity or STR) is the accepted physical theory regarding the relationship between space and time. It is based on two postulates. Which of the following are the two postulates of the special theory of relativity?
a) The laws of physics are invariant in all inertial systems.
b) The speed of light in a vacuum is the same for all observers, regardless of the motion of the light source.
c) The length of an object which is traveling at any non-zeo velocity relative to an observer decreases when it is measured by the observer.