Answer:
According to the theory of special relativity, as an object approaches the speed of light relative to an observer, its length appears to decrease from the perspective of that observer. This phenomenon is known as length contraction. Therefore, if an object is moving with a velocity that approaches the speed of light relative to a stationary observer, the length of the object appears less than its rest length to the observer. Hence, the correct option is:
The length of the moving object appears less than its rest length.