Section B
Directions: There are 2 passages in this section．Each passage is followed by some questions or unfinished statements．For each of them there are four choices marked A, B, C and D．You should decide on the best choice.
In the wild, chimpanzees have been known to hunt together, particularly when conditions dictate that a solo hunter will not be successful．Yet this does not prove that our nearest living relatives understand cooperation the same way that we do: such group hunts may simply be the product of independent and simultaneous actions by many individuals with little comprehension of the need for coordinated action to ensure success．A new study, however, shows for the first time that chimpanzees understand when cooperation is needed and how to go about securing it effectively．And another study shows they might even be willing to cooperate without hope of reward.
Alicia Melis of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and her colleagues presented chimpanzees at a sanctuary(保护区)in Uganda with a cooperative challenge．To reach a food tray from behind bars, a chimpanzee had to pull on two ends of a rope threaded through metal loops on the tray．If the chimpanzee simply pulled on one end, the rope would slip the loop．If, however, the chimpanzee unlocked the door to an adjacent room, released a fellow chimp, and cooperated with it to pull on both ends of the rope at the same time, both would be rewarded with the food on the tray.
Although this provides the first glimpse of cooperative understanding outside humanity--and raises the possibility that such abilities might have been present in our common ancestor more than six million years ago--it does not mean that chimpanzees can communicate about a shared goal, like human children．However, in the second study, led by Felix Warneken, also at the Max Planck Institute, three young chimpanzees helped their human minder reach for objects even without any hope of reward--just like human children as young as 18 months old．'This is the first experiment showing altruistic helping toward goals in any nonhuman primate(灵长类动物),' Warneken notes．'It's been claimed chimpanzees act mainly for their own ends, but in our experiment, there was no reward and they still helped.'
In the animal world, chimpanzees were believed ______.