The correct answer is B) 225.0°. The compass course of a vessel heading SW (southwest) is 225.0°. This is because the southwest direction falls between the cardinal directions of south (180°) and west (270°), and the midpoint between these two directions is 225.0°. The other options are incorrect because: A) 202.5° is too far to the south, C) 247.5° is too far to the west, and D) 270.0° is directly west, not southwest.