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.
单选题
【C1】
【正确答案】
B
【答案解析】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”。
单选题
【C2】
【正确答案】
A
【答案解析】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theirsurvival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……”。
单选题
【C3】
【正确答案】
C
【答案解析】解析：第一段最后一句but之后谈到大象的嗅觉无疑也是最灵敏的(most effective)，而空格之后却说人类(human)等的嗅觉不怎么灵敏(poor sense of smell)。可见前后有对比含义，incomparison意为“相比之下”，符合句意，选C项comparison。
【答案解析】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 ele-phants“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。