Final answer:
The flattest part of the ocean is the Abyssal plain.
Step-by-step explanation:
The flattest part of the ocean is the Abyssal plain. It is a flat, featureless plain located at the deepest parts of the ocean basins. The abyssal plain is found at an average depth of about 4,000 to 6,000 meters and covers a significant portion of the seafloor.
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