From approximately 240 to 66 million years ago, dinosaurs dominated most of the land habitats on Earth. Around 66 million years ago, most dinosaurs went extinct when an asteroid struck the Earth. Mammals, which were much smaller and lived primarily in underground habitats, were able to avoid extinction. Mammals then underwent an adaptive radiation to develop a wide variety of new species.

Which of the following is an advantage of using embryonic stem cells in medical research? a. the use of embryonic stem cells is much less expensive than the use of adult stem cells. o b. no living tissue is damaged when scientists use embryonic stem cells. o c. embryonic stem cells are able to differentiate into a wider range of cells than adult stem cells. d. there is no controversy surrounding the use of embryonic stem cells.