The Most Important Reason an Object Is Observed to Be

Multiple Choice

The most important reason an object is observed to be shorter in a frame where it is moving than in a frame where it is at rest is that

A) The force of motion strongly compresses an object that is moving at relativistic speeds.
B) "Simultaneity" is not a frame-independent concept.
C) The measuring sticks used by the moving observer are Lorentz-contracted.
D) The clocks used by the moving observer run slower.