The correct answer is C) P. The preferred knot for securing a line to a spar when the pull is parallel to the spar is the Clove Hitch, which is labeled as "P" in the illustration. The Clove Hitch creates a secure attachment that can withstand a pulling force parallel to the spar, making it the most appropriate choice in this scenario. The other options, such as the Bowline (G) or Figure-Eight (F), are not as well-suited for this specific application, as they may not provide the same level of stability and resistance to the parallel pull.