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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 smeD 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.
【C2】
选项 A、to
B、in
C、by
D、through
答案A
解析 空格前的部分how important it is说明象鼻(trunks)很重要，空格后的部分their survival意为“大象的生存”。可以看出，前者是相对于后者而言，下文的具体例子可以佐证，故选A项to“对于……”。
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