Elephants are famous for their supposedly excellent memory. Now it seems that they are go

Elephants are famous for their supposedly excellent memory. Now it seems that they are good at simple math too.
Researchers at the University of Tokyo have found an Asian elephant named Ashya can add small quantities together and correctly identify(识别）which is larger.
For example ,when researcher Naoko dropped three apples into one bucket and one apple into a second, then four more apples into the first and five into the second, Ashya correctly identified that the first bucket contained more apples and began munching(嚼）on her tasty prize.
Ashya chose the correct bucket 74% of the time I even get confused when I'm dropping the apple, Naoko told New Scientist magazine.
Elephants' counting abilities are far from unique. Chimps, pigeons(鸽子)and dolphins have shown the same abilities in lab tests, but what is more impressive for Elephants is that their ability to tell between two figures does not get worse when those numbers are more similar.
The elephants that Naoko tested were as good at telling the difference between five and six as they were at telling between five and one.
Naoko presented her findings last week at the International Society annual meeting in New York.
It is not obvious why elephants should need this mathematical ability in the wild. It is really tough to figure out why elephants would need to count, said Mya, a professor at Cornell University who studies elephants.
One possibility is that they use it to keep track of other members of their herd(兽群）so that no one is left behind. Asian elephants live in groups of six to eight. You really don't want to lose your group members, said Mya.
Another possibility is that the ability for simple math might be a by-product(副产品）of natural selection for a larger brain.
68.The experiments researchers have done recently show that elephants can    .
A. memorize things correctly      B. munch on apples
C. do some simple math          D. change small quantities into larger ones
69.What does the underlined word tough in Paragraph 8 mean?
A. Difficult        B. Impossible     C. Easy      D. Useful
70.The reason why elephants need to count is possibly that    .
A. they want to exercise their brains
B .they often count the members of their herd
C. they hope to stay in groups
D. they have taken regular training68~70 CAB