Answer:
a. continental shelf
Explanation:
It has been stated in the question that the shelf of undersea land reaches 200 meters and it also extends out from the shoreline. This condition is only possible when a structure is submerged. This is only possible for the continental shelf. On the other hand, abyssal plains are formed deep inside the sea (depth of 3000 to 6000 meters). Deep-sea trenches are further deep-sea structures formed between 7,300 to 11,000 meters depth. These are also called oceanic trenches. Lastly, guyots are mountains with flat top inside the sea and are present at least 200 m below the sea level. Therefore, the condition of being submerged is only satisfied for the continental shelf.
