Task: Question Answering
Input (English): Background Paragraph: Einstein showed in his thought experiments that people travelling at different speeds, while agreeing on cause and effect, measure different time separations between events, and can even observe different chronological orderings between non-causally related events. Though these effects are typically minute in the human experience, the effect becomes much more pronounced for objects moving at speeds approaching the speed of light. Subatomic particles exist for a well known average fraction of a second in a lab relatively at rest, but when travelling close to the speed of light they are measured to travel farther and exist for much longer than when at rest. According to the special theory of relativity, in the high-speed particle's frame of reference, it exists, on the average, for a standard amount of time known as its mean lifetime, and the distance it travels in that time is zero, because its velocity is zero. Relative to a frame of reference at rest, time seems to "slow down" for the particle. Relative to the high-speed particle, distances seem to shorten. Einstein showed how both temporal and spatial dimensions can be altered (or "warped") by high-speed motion. 
Story: David wanted to test the theory of Einstein. To that end, he measured the time perceived by an airline pilot, who naturally traveled very fast. He labeled it as case A. To compare the pilot with a slower traveler he measured the time perceived by a semi truck driver covering the same distance. He labeled it as case B. He was amazed by the counter intuitive results he got from the experiment. 
Question: According to Einstein, who would perceive "slow down" of time, case A or case B?
Output (English): case A.