When b sees that a is rising at a constant speed, it means that b is also falling, and the speed of decline is faster than a,
A sees C falling at a constant speed, which means C is falling faster than A. 。
B feels windless, which means that B runs as fast as the wind, which means that the wind is westerly.
A feels downwind, which means that A runs slower than the wind.
C feels against the wind, which means C runs faster than the wind.
Therefore, taking B as the reference, A- direction-west-movement, C- direction-east-movement.