The correct answer is B) to prevent chafing at the lower end of the pendant. The design of a spring buoy, which is a type of mooring buoy, helps prevent chafing or abrasion at the lower end of the pendant (the line or chain connecting the buoy to the anchor or mooring point). The spring action of the buoy absorbs the up-and-down movement of the tide and waves, reducing the strain and wear on the pendant and preventing it from rubbing against the seafloor or other surfaces. The other answer choices are incorrect because they do not accurately describe the primary function of a spring buoy. Option A refers to marking the approach to a rig, which is not the purpose of a spring buoy. Option C describes the function of an anchor handling vessel, which is unrelated to the design of a spring buoy. Option D mentions retrieving the anchor, but a spring buoy's main role is to protect the pendant, not to facilitate anchor recovery.