Final answer:
A guyot is a seamount with a flattened top formed by volcanic activity and subsequent erosion. It is different from other features like trenches, continental shelves, and abyssal plains. The correct answer is option d.
Step-by-step explanation:
The term that is described as a seamount with a flattened top is known as a guyot. Guyots are typically formed by underwater volcanic mountains that, after becoming extinct, are eroded by wave action and flattened. Guyots contrast with other oceanic features such as trenches, which are deep depressions often associated with convergent plate boundaries, and the continental shelf, which is the submerged edge of a continent, typically in shallow waters. Abyssal plains are flat or very gently sloping areas of the deep ocean basin floor. Seamounts, before being flattened to become guyots, are formed as the oceanic plate moves over a hot spot, creating underwater mountains.