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  3. If you have ever wondered how an elephant smells, scientists have the answer. Researchers have discovered that African Elephants

If you have ever wondered how an elephant smells, scientists have the answer. Researchers have discovered that African Elephants

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问题     If you have ever wondered how an elephant smells, scientists have the answer. Researchers have discovered that African Elephants have the largest number of genes【C1】______smell of any mammal. Given the size of their trunks, and how important it is【C2】______their survival, it is probably unsurprising that an elephant’s nose is not only the longest in the animal kingdom, but also the most effective.
    In【C3】______, humans and other primates have a poor sense of smell. "The functions of these genes are not well known,【C4】______they are likely important for the living environment of African elephants," said author Dr Yoshihito Niimura of the University of Tokyo. "【C5】______, an elephant’s nose is not only long but also superior. " The sense of smell is【C6】______to all mammals, and they use it for【C7】______food, finding mates and locating their offspring.
    In a study published in Genome Research, scientists【C8】______the 13 mammal species and found that African Elephants have twice the number of smell genes【C9】______dogs and five times more than humans. They have around 2,000 genes alone that are associated with scent. Humans in comparison have just under 400 and some other primates even【C10】______. The study found that 20,000 genes are【C11】______for the sense of smell in mammals, of which around half are functional, but the collections【C12】______for each species. Horses have around 1,000 smell genes, rabbits around 750 and rats about 1,200.
    "The large repertoire of elephant (smell) genes might be attributed to elephants’ heavy【C13】______on scent in various contexts, including social【C14】______and reproduction," added Dr Niimura. African and Asian elephants possess a【C15】______scent organ behind each eye, and male elephants can produce a special substance during annual mating, which is characterized【C16】______increased aggressiveness. And【C17】______studies have revealed that, African elephants can reportedly【C18】______between two Kenyan ethnic groups—the Maasai, whose young men【C19】______manhood by spearing elephants, and the Kamba, who are agricultural people that【C20】______little threat to elephants through smell.
【C13】
选项 A、endurance
B、ignorance
C、disturbance
D、reliance
答案D
解析 本句已知的句意为“大象拥有如此众多的嗅觉基因是因为大象在各场合对气味……”，根据第二段第二句they are likely important for the living environment of African elephants“它们(嗅觉基因)对非洲象的生活环境很重要”可知，大象很需要这些嗅觉基因。故选D项reliance“依赖”。与空格后的介词on搭配．表明大象对气味的依赖。
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