Polar Dinosaurs When You Think of the Typical Dinosaur Habitat, Images of Images

Polar Dinosaurs
When you think of the typical dinosaur habitat, images of steamy swamps or boiling tropical forests probably come to mind. And certainly, dinosaurs flourished in such environments for millions of years. You might not think of Antarctica or Alaska as probable homes for dinosaurs. However, paleontologists have unearthed the remains of dinosaurs that did quite well in environments that were cold for at least part of the year. Known as polar dinosaurs, they endured long periods of darkness, sometimes up to six months each winter.
Seventy million years ago, Alaska was cold but not as cold as it is today. Still, winters would have come with plenty of ice and snow. Scientists estimate that Alaska's climate at the time would have come close to that of Chicago today. The fossil evidence shows that relatives of Tyrannosaurus rex would have hunted the thirty-five-foot-long herbivore Edmontosaurus in forests rich with conifers, or cone-bearing trees, such as ancestors to modern junipers or pines.
Polar dinosaurs had two options when winter arrived. They could stay put or escape to warmer climes. Amazingly, it appears that some remained in the area over the long winters. This raises the question of whether the polar dinosaurs were warm-blooded, like modern birds and mammals, or cold-blooded, like modern reptiles. Warm-blooded animals maintain body temperature internally, through metabolism. By contrast, cold-blooded animals warm their bodies by absorbing heat from the sun and their surroundings. That's why you might see a lizard sunning itself on a rock early in the morning. But, at extreme northern and southern latitudes, the sun doesn't rise for several months during the winter. In these places, it would be nearly impossible for a cold-blooded dinosaur to survive. Could these dinosaurs have actually been warm-blooded?
Common sense says that they had to be warm-blooded. And many paleontologists now agree. To see why you just need to look at the bones. Bones of all animals have growth rings, similar to the growth rings found on trees. They indicate how quickly or slowly an animal grows. The researchers compared the dinosaurs' growth rates with those of both living and extinct animals and found that the dinosaurs' growth rate matched that of mammals. Scientists also looked at limb length and the amount of muscle required to move the limbs. Cold-blooded animals typically have shorter limb length and less muscle mass than warm-blooded animals. Based on hip height, these scientists concluded that the five largest dinosaurs would have had to be warm-blooded to walk or run. The polar dinosaurs lived in a very strange world. And many scientists now think that the only way they could have thrived there was by being warm-blooded.
Warm-blooded animals maintain body temperature internally, through metabolism.
What is the author's purpose for the following sentence above?

A) To support the idea that some animals thrived in warmer climates
B) To suggest that warm-blooded animals can be more successful than cold-blooded ones
C) To provide the reader with a definition of "warm-blooded"
D) To contrast polar dinosaurs with dinosaurs that lived in warmer areas