Ashining light casts a horizontal beam through a spacecraft.

which two observers would see this beam of light in the exact same way?

a. an observer inside the spacecraft while the spacecraft is at rest and an observer inside the spacecraft while the spacecraft is moving at a constant velocity
b. an observer inside the spacecraft while the spacecraft is accelerating and an observer inside the spacecraft while the spacecraft is at rest
c. an observer on earth while the spacecraft is at rest and an observer inside the spacecraft while the spacecraft is at rest
d. an observer on earth while the spacecraft is at rest and an observer inside the spacecraft while the spacecraft is moving at a constant velocity