根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
Penguins are flightless birds that spend half their time on land and half in the water.
They have dark and white feathers, and their wings have evolved into flippers(脚蹼).Most penguins feed on fish, squid and other forms of sea life caught while swimming.
They are mostly found in groups that include thousands of penguins. Penguins each have their own unique mating call, and they use that to locate their mate and chicks in such a large group.
Although almost all penguin species are native to the Southern Hemisphere, they are not found only in cold Antarctica. Several species are even found in the temperate zone, and one species, the Galátpagos penguin, lives near the equator(赤道).
Unfortunately, many penguin species worldwide are facing threats. The biggest is climate change and global warming. As the earth warms up, the sheets of ice have melted, and the algae(藻类)that grow under the ice decrease. The algae are eaten by tiny creatures called zooplankton. When there is a drop in zooplankton, it affects the fish that depend on it.
Another major threat is from oil spills. If coated with oil, penguins cannot float or swim in water. Also, if oil is swallowed, penguins will die from poison.
A. These birds are very social.
B. In fact, only a few of them live so far south.
C. Penguins are highly adapted for life in the water.
D. The biggest threat for penguins comes from humans.
E. They have a tendency to live in a community together.
F. As a result, penguins have less fish to eat and thus starve.
G. Others include overfishing, illegal egg harvesting, and natural enemies.