A, B and C ride bicycles on the same road to the north, so they move in the same direction. Taking air as a reference, C feels downwind, which means that the speed of C is less than that of the wind. A feels calm, which means that the speed of A is the same as that of the wind. B feels the headwind, which means that B's speed is greater than the wind speed. To sum up, B is the fastest and walks the fastest; C has the slowest speed and walks the slowest. So the wind direction is north wind. Take car A as the reference, car B to the north, car A as the reference, car C to the south, and car A to the wind as the reference. So option C is correct and ABD is wrong.
So I chose ABD. ..