D is the answer to this question. The PSI stands for Pound-force per square inch. This is known as one of the units of pressure. This is used in different ways. One of the most notable ways that this is used is whenever people dive. They usually bring tanks of oxygen with them that contain a certain PSI.
Take note that the reading of this will always differ when they are already at sea level. There are some divers who will determine if they already need to go resurface if they do not have enough PSI left. They can make the PSI last longer if they would know their actual weight. They can make adjustments depending on their needs.