问题：

[共享题干题]How generous is an ape? This generosity may have been______(91) to the survival of our early ancestors______(92) lived in small bands of hunter-gatherers. Dr. Krupenye and his colleagues tested the generosity of bonobos. The researchers designed an experiment that could provide strong evidence that bonobos could give things to each other simply______(93) generosity - rather than being pressured into doing so, or expecting some sort of immediate payback. For their experiment, the researchers______(94) advantage of the fact______(95) the Lola Ya Bonobo apes have learned to crack open palm nuts with rocks.______(96) a rock, they have to gnaw on the nuts for a long time to get them out of their shell. The scientists put one bonobo in a cage with five nuts. In an adjacent cage, a______(97) bonobo - a stranger to the first one - had two rocks but no nuts. The cages were connected by a window. The bonobos were free to bring gifts to the window______(98) to each other - or to ignore their______(99). The researchers found that the bonobos with the nuts proved generous. In 18 percent of the trials, the bonobos with the nuts handed one through the window to their neighbor, a rate that showed their______(100)to give food to others. But the bonobos in the other cage almost______(101) returned the favor. They refused to pass one of their rocks through the window. In______(102) experiment, Dr. Krupenye experienced their______(103) of generosity firsthand.Each bonobo would sit in a cage, with a mesh wall ______(104) in front of the door to the hallway. A colleague would ______(105) a stick into the cage near the bonobo and leave. Then Dr. Krupenye would come to the doorway and beg for the stick. He would reach ______(106) his arm, plaintively calling the bonobo’s name. The bonobos almost never handed Dr. Krupenye the stick. In fact,sometimes they seemed to tease him. “They will put it through the mesh a little bit and then pull it back when I’m trying to reach for it," said Dr. Krupenye. The work of Dr. Krupenye and others makes______(107) clear that humans aren’t unique in their generosity. It’s possible that our common ancestor with bonobos and chimpanzees was already prosocial, at least______(108) a limited extent. This versatility may have______(109) early in our lineage, producing traits that encouraged more sharing. It leads______(110) to have generous inclinations without any coaching.
单选题第1题How generous is an ape? This generosity may have been______(91)
A.special
B.extraordinary
C.extreme
D.crucial