A、By the meaning of words. B、By the tone of speaking. C、By the gender of speakers. D、By the changes of phrases. B短文最后提到，大象不会理解人们

They say that elephants never forget; it turns out they can also tell the difference between human languages! Elephants don’t have the best eyesight in the animal kingdom, but they make up for it with their intelligence. Scientists already know they are very smart— elephants never forget a face and that’s where the saying came from, but they didn’t know just how smart until this recent study. Researchers played recordings of human voices for 47 herds of elephant families at Amboseli National Park in Kenya over a two-year period. The recordings were from Maasai adults and children, and Kamba men. The Maasai are an aboriginal tribe who sometimes come into conflict with elephants over water and land that sometimes leads to the death of elephants or Maasai men. The Kamba people usually work as farmers or employees for the park and rarely cause harm or danger to elephants. They speak Kikamba. When the elephants heard Maasai men saying “Look, look over there, a group of elephants is coming,” they gathered together, started smelling curiously with their trunks, and cautiously moved away to avoid confrontation. But when they heard Maasai women or boys, or adult male Kamba speakers they didn’t show any concern. The ability to distinguish between Maasai and Kamba men delivering the same phrase in their own language suggests that elephants can discriminate between different languages. They can’t understand what the words mean, but they can associate a certain way of speaking, like vowels or inflections with a possible threat.
16. What can we know about elephants?
17. How will elephants respond after hearing Maasai men saying “Look, look over there, a group of elephants is coming”?
18. How do elephants judge the threat posed by humans?