D. Two sizes of bullet points distinguish between two levels of information.
Here the bullets are used for two different things. The first bullet is part of the list of things you should do to prepare your car for going on a long trip. Those things include taking your car for a tune-up, making sure you have a spare tire, and packing an emergency car kit. The second bulleted list contains all of the items that should be inside the emergency car kit. The first level is the tier that directly relates to things that should be checked before a long trip. The second level expounds on what is to be in the emergency car kit.