The correct answer is D) Coriolis force. The Coriolis force is the key factor that deflects the wind flow from the horse latitudes to the doldrums. The Coriolis force is an apparent force that arises due to the Earth's rotation, causing moving objects like air masses to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection is what causes the wind patterns between the horse latitudes and the doldrums. The other answer choices are incorrect because they do not directly cause the deflection of the wind flow in this specific scenario. The prevailing westerlies, differing atmospheric pressures, and the mid-latitude, semi-permanent high are all important factors in global wind patterns, but they do not directly account for the deflection observed between the horse latitudes and the doldrums.