单项选择题

TEXT E
As the hot arctic summer drew to a close, till the magenta sun only slid along the horizon to sink again at once, the polar bear knew that a hard time lay ahead for her.
During the months of night, fifty degrees below zero, her cubs would be born, the great task of motherhood was already begun, the time soon coming when she would bury herself deep down under the snow to give birth. From then until the day when she and the cubs burrowed up into daylight again she would not eat. She and they must live on what she had stored in her body during the summer, and on what she could catch and eat now. She must finish fattening herself up for the ordeal, and there was not much time left.
She was not clearly aware of what was happening in her body, but the instinct was there to love the unborn cubs, to prepare for them and protect them; she did not risk her body in careless adventures as she would at other times.
But food Food--
Suddenly, away down the ice-field, she saw a blackish slug on the ice--a seal. It was essential to catch him. In a moment she had decided on her approach, and slipped silently into the water to cut off his line of retreat. The ice rocked as her great weight left it.
By a series of cunning dives and approaches, and keeping under the shoulder of ice, she got near to the seal. Breathing carefully, every nerve keyed to the task of silent approach, ready to spring--to dive--to slaughter, she slid nearer---nearer---
Suddenly the seal saw her. Terror convulsed his face.
He swung away from her, humping madly along. The bear lunged up out of the water, on to the ice, on to the terrified seal.
The water slashed off her everywhere like a tidal wave. There was a flurry of snow and water and fighting seal. His quick struggling body flapped under her as she slew him. Blood spurted on to the snow.
When the seal was dead, the bear attended first to herself, getting rid of the wet from her coat before it could freeze, although oil had kept off the frost so far.
Now for the seal. She ripped up the body, turning back the skin and blubber, letting out a cloud of steam, and ate greedily of the hot crimson meat. Seal meat was her favorite, full of flavor, a hot meal, not like the white icy flakes of cod.
Presently she saw upright seals coming along the shore. They were rather rare creatures, these, and dangerous for all they were so weak. The places where they lived had light and noise, and smelled full of good food. The she-bear often drew near the places, attracted by those smells. She hunted these land-seals too, and ate them when she could. They were not like the sea-seals, though. They wore seal fur, and their skins were rubbed with seal blubber, but there was a different taste inside.
The upright seals mentioned in the last paragraph were ______.