A、Horses. B、Rats. C、Dogs. D、Rabbits. B

If you have ever wondered how an elephant smells, scientists have the answer. Pretty good. Researchers have discovered that African elephants have the largest number of DNAs dedicated to smell of any mammal. Given the size of their trunks, and how important it is to 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 comparison, humans and other animals have a poor sense of smell. (16) The sense of smell is critical to all mammals, and they use it for sniffing out food, avoiding being killed by other animals, finding mates and locating their offspring. (17-1) In a study published in Genome Research, scientists examined the 13 mammal species and found that African elephants have twice the number of smell DNAs as dogs and five times more than humans. They have around 2,000 DNAs alone that are dedicated to scent. Humans in comparison have just under 400 and other animals, even less. The study found that 20,000 DNAs are responsible for the sense of smell in mammals, of which around half are functional, but the collections differ from each species. (17-2) Horses have around 1,000 smell DNAs, rabbits around 750 and rats about 1,200. (18) And previous studies have revealed that, African elephants can reportedly distinguish between two Kenyan ethnic groups—the Maasai, whose young men demonstrate their manpower by spearing elephants, and the Kamba, who are agricultural people that pose little threat to elephants—through smell.
16. Why is the sense of smell important for mammals?
17. Which of the following mammals has the largest number of smell DNAs?
18. What benefit can African elephants get by telling the difference between the two ethnic groups?