Fill in the blanks using one of the words: at rest, in motion.

(a) A person walking in a compartment of a stationary train is ………………. relative to the compartment and is ………………. relative to the platform.

(b) A person sitting in a compartment of a moving train is ……………….. relative to the other person sitting by his side and is ………………….. relative to the platform.

(a) in motion, in motion

(b) at rest, in motion