Many people like the gigantic whales. Human sympathy 【C1】______ whales is

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问题      Many people like the gigantic whales. Human sympathy 【C1】______  whales is only natural of all the creatures in the sea. 【C2】______  are closer relatives to us than these warm-blooded mammals. And how they got into the sea is one of the most fascinating stories of 【C3】______  . Most authorities believe that 60 million years ago ancestors of modern whales were four-legged, wolf-size animals living on the sea shores, 【C4】______  an abundance of fish and shrimp tempted them to try wading. Over 10 to 15 million years, their bodies grew, forelegs shrank into flippers used for 【C5】______  and steering and hind legs disappeared. As a result of some amazing transformations, they arc now helpless on land. If stranded on a beach, they can barely breathe.
   With abundant 【C6】______  of food, whales grew into the largest creatures that lived, 【C7】______ larger than dinosaurs. A blue whale can grow to 100 feet. Its tongue is ten feet thick and heavier than an elephant. Some arteries are big enough for a child to swim 【C8】______  . The half-ton heart has walls two feet thick and pumps eight tons of blood. 【C9】______  its size comes awesome strength. A blue whale swimming 【C10】______  15 knots generates 1000 horsepower. 【C11】______  their size, these giants move at a good speed. An 18-ton whale can even 【C12】______  12 m. p. h., over short distances. A whale can 【C13】______  up to 9000 pounds of food a day. The world’s biggest creature 【C14】______  itself almost entirely on shrimp-like krill, smaller than a person’s thumb.
   Maternal instincts are also highly 【C15】______  . Because a calf is born underwater, the mother must get it to the surface before it 【C16】______  . Often another whale will help. The mother pushes it gently 【C17】______  the baby is confident with its swimming usually after about 30 minutes. If the calf is born 【C18】______  , she may support it on her back until it gradually rots away. Like all mammals, whale babies feed 【C19】______  mother’s milk. And the milk is more than 30-percent fat, over 10-percent protein, and the babies grow extremely fast. A blue whale calf lengthens 【C20】______  two inches a day and gains an average seven pounds per hour.  [br] 【C17】

选项 A、until
B、but
C、while
D、unless

答案 A

解析 连接词辨析题。根据句意,鲸鱼妈妈轻轻地推着小鲸鱼游动,直到小鲸鱼对自己的游泳技术很有信心为止,所以应选择连词until“直到……才”。B)but“但是”,C)while“当……的时候”和D)unless“如果不,除非”均不符合句子逻辑关系,可以排除。
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