What is a central idea of the passage? from The Unicorn of the Sea
ic and Atmospheric Administration

OA Whales are difficult to study because they are found in waters that are difficult to reach and covered in ice.

OB. The narwhal is a deep-water diving marine mammal with a single tooth, or tusk, for which it is best known

OC The narwhal has a single tooth, outside of its mouth, unlike other marine mammals, who have many teeth.

OD Whales, such as the narwhal, that inhabit Arctic waters feed mainly during the spring and summer months.