Question

the dumbo octopus lives deeper under the sea than any other octopus species, hovering just above the seafloor. the particular part of the ocean where the dumbo has been documented reaches depths of about three to eleven kilometers under the surface of the ocean. at these depths, sunlight does not penetrate the water, creating a cold and dark atmosphere. scientists rarely have the opportunity to visit these mysterious locations, as deep - sea trips tend to be much longer and more expensive than exploratory jaunts that stay closer to the surface.
since its deep - sea home is rarely visited, sightings of the dumbo octopus are incredibly rare. it has been spotted in tropical and temperate waters across the globe, from new zealand and australia to papua new guinea, as well as off the coasts of california and oregon. compared with other octopuses, a dumbo can easily be missed because of its relatively small stature. when dumbo octopuses are spotted, researchers have measured these cephalopods to be around eight to twelve inches long. the largest dumbo octopus was more than six feet (two meters) long and weighed thirteen pounds (six kilograms), but most are on the smaller end of the scale.
which statement best analyzes the purpose of the footnote in passage 3, paragraph 3?
the author included the footnote to explain why sunlight does not reach the depths where the dumbo octopus is found.
the author included the footnote to highlight the rarity of scientists visiting these depths by emphasizing the vast distance.
the author included the footnote to describe the cold and dark atmosphere of the dumbo octopus’s habitat.
the author included the footnote to help readers understand the extreme depths at which the dumbo octopus lives with a familiar unit of measurement.

Explanation:

The footnote converts kilometers (3-11 km underwater) to a more familiar unit for readers to grasp the extreme depth. The other options are incorrect: the passage already states sunlight does not reach these depths without needing the footnote for that explanation, the footnote does not highlight scientist visit rarity, and it does not describe the habitat atmosphere.

Answer:

D. The author included the footnote to help readers understand the extreme depths at which the Dumbo octopus lives with a familiar unit of measurement.