The correct answer is: B. west
Rain is falling vertically downwards. To a man running east-wards, the rain will appear to be coming from west because the man is moving towards the east and the rain is falling vertically downwards. The rain will appear to be coming from the west because the man is moving towards the east and the rain is falling vertically downwards. The man is moving towards the east, so the rain will appear to be coming from the west.
Option A is incorrect because the man is moving towards the east and the rain is falling vertically downwards. The man is not moving towards the west, so the rain will not appear to be coming from the east.
Option C is incorrect because the man is moving towards the east and the rain is falling vertically downwards. The man is not moving towards the northeast, so the rain will not appear to be coming from the northeast.
Option D is incorrect because the man is moving towards the east and the rain is falling vertically downwards. The man is not moving towards the southeast, so the rain will not appear to be coming from the southeast.