All penguins (企鹅) swim in cold waters and so need a good layer of insulation (隔离), some species come ashore in hot places.Humboldt penguins,for example,nest in arid hot - 40°C, deserts on the west coast of South America, while others survive the lowest temperatures of any animals.Male Emperor penguins,as we know, spend the Antarctic winters incubating eggs in temperatures that can fall below -70°C. The insulation is provided in layers, under the skin is a thick layer of fat, then there is a layer of downy feathers that trap air, and finally another layer of waterproof feathers that keep the cold water away from the skin. With all this insulation penguins have no problem keeping warm at temperatures down to about -10°C - although they have special adaptations of the circulatory system to keep their feet from freezing and to prevent much heat loss through the feet that are on the ice. At lower temperatures penguins have to huddle (蜷缩) together to keep warm. In such huddles the penguins gradually move from the hot interior to the cold outside so that every penguin has his turn in the middle and on the outside.
In hot climates, penguins suffer greatly from overheating. They use several strategies to lose heat. They puff up their feathers so that air can circulate to their skin; they hold their flippers（脚蹼）out from their bodies and pump hot blood to them so that they can act as radiators; they open their mouths and breathe to lose heat from their hot breath; and those species that live in hot climates also have several bare patches of skin around the eyes and feet, they send blood to these bare patches when they are hot - you can recognize a hot penguin since it will have pink eye patches and pink patches on its feet.
77. Which of the following are the ways for penguins to keep warm?
a. staying together in good social order 
b. several layers as radiators
c. a special circulatory system                    d. waterproof feathers
e. sending blood to bare patches
f. always staying in the middle
A. a, b, c                    B. a, c, d                    C. b, c, e                    D. c, d, f
78. The insulation consists of _______ layers.                                       
A. two                        B. three                      C. four                       D. five
79. The underlined "puff up" in the second paragraph can be replaced by ______.
A. breathe deeply         B. blow up                 C. hold tight               D. spread out
80. The passage mainly tells us ______.
A. how penguins stay warm in cold places       B. that penguins are a clever animal
C. how penguins keep their temperature          D. why penguins can live a safe life