Question ID:PT26 S2 Q14 Passage:The common ancestors of Australian land- and tree-dwelling kangaroos had prehensile (grasping) tails and long opposable thumbs, attributes that are well-adapted to tree-dwelling but offer kangaroos few advantages on land.  It is hardly surprising, therefore, that land-dwelling kangaroos eventually lost these attributes; what is puzzling is the fact that all modern tree-dwelling kangaroos now lack them as well. Stem:Which one of the following, if true, most helps explain the puzzling fact cited above? Correct Answer Choice:DChoice A:Modern tree-dwelling kangaroos must back down tree trunks slowly and carefully, but the common ancestors of modern tree- and land-dwelling kangaroos used their opposable thumbs to descend trees quickly headfirst. Choice B:Modern tree-dwelling kangaroos are smaller than most modern land-dwelling kangaroos but larger than their common ancestors. Choice C:Modern tree-dwelling kangaroos' tails cannot grasp branches, but they are somewhat longer and more flexible than those of modern land-dwelling kangaroos. Choice D:Modern tree-dwelling kangaroos are descended from species of land-dwelling kangaroos that had been land-dwellers for many generations before modern tree-dwelling kangaroos started to develop. Choice E:Modern tree-dwelling kangaroos have smaller and weaker hind legs than modern land-dwelling kangaroos, and they move more slowly on land than do modern land-dwelling kangaroos.