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.
【C1】

选项 A、given out
B、dedicated to
C、limited to
D、hit upon

答案B

解析 空格要求填入过去分词作后置定语修饰宾语the largest number of genes(最大数量的基因)。后置定语中的名词为smell(嗅觉),从“基因决定机能”的常识可知,空格前的genes决定着空格后的smell。B项dedicated to意为“专注于;把……用在”,此处意为“嗅觉基因”。
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