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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.
【C11】
选项 A、helpful
B、responsible
C、suitable
D、ready
答案B
解析 上文提到大象有2,000个基因有助于嗅觉(are associated with scent)，此句继续扩展讨论哺乳动物有关基因和嗅觉的话题。responsible for意为“对……负责”，此处指有2万基因对嗅觉负责，即与嗅觉相关，故选B项responsible。如果选A项helpful“有助的”，表明这些基因对嗅觉只是起到辅助功能，表达不确切。C项suitable“合适的”，表示有选择性，而基因并不可选择。D项ready“随时准备的”，be ready for sth.意为“准备好随时做某事”，基因显然不具备此特征，故不合逻辑。
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