I think its D im not sure hope this helped
<span>Guyots are seamounts that have built above sea level. Erosion by waves destroyed the top of the seamount resulting in a flattened shape. Due to the movement of the ocean floor away from oceanic ridges, the sea floor gradually sinks and the flattened guyots are submerged to become undersea flat-topped peaks.</span>
The Prime Meridian marks zero degrees longitude. Without it, the other degrees of longitude cannot be measured.
D. Obviously because it was large and they didn't have a lot of supplies to go across also it was very deep.
