单项选择题

Some people say that seals are the fairies of the sea and should not be killed. The seals are the cleverest creatures that have ever been found in the sea. "In the Kingdom of the Seals" is an English fairy story by Donald A. Mackenzie, which tells of a seal hunter who wounds a seal. The seal swims away with the hunter"s knife still in its back. That evening a stranger on a black horse calls at the home of the seal hunter and takes him to the edge of a cliff. Suddenly the seal hunter finds himself falling. He falls to the bottom of the sea.
The stranger changes into a seal and leads him towards a huge underwater palace. Inside the palace he sees an old grey seal lying on a bed in terrible pain. Beside the bed is a knife, which the hunter recognizes as his own. He is ashamed of his cruelty and begs forgiveness of the old seal. Soon the wound is healed when the seal hunter lays his hand on it and wishes. The old seal regains his strength straight away. The seal hunter promises never to hunt seals again. Then he is led back to dry land. When he gets home he finds his pockets are filled with pearls.
In reality, true seals are earless. There are 18 species of careless seals. Fur seals are not true seals. Fur seals feed mainly on a small type of shrimp. When diving for food seals have been known to reach depth of 300 meters, but throughout the breading season of several weeks, male seals do not eat or drink. The purpose of writing the passage is that