The fossil record shows that the climate of North America warmed and dried at the end of the Pleistocene period. Most of the species of large mammals then living on the continent became extinct, but the smaller mammalian species survived.
Which of the following, if true, provides the best basis for an explanation of the contrast described above between species of large mammals and species of small mammals ？（）
A．Individual large mammals can, in general, travel further than small mammals and so are more able to migrate in search of a hospitable environment.
B．The same pattern of comparative success in smaller, as opposed to larger, species that is observed in mammals is also found in bird species of the same period.
C．The fossil record from the end of Pleistocene period is as clear for small mammals as it is for large mammals.
D．Larger mammals have greater food and space requirements than smaller mammals and are thus less able to withstand environmental change.
E．Many more of the species of larger mammals than of the species of smaller mammals living in North America in that period had originated in climates that were warmer than was that of North America before the end of the Pleistocene period.