Why are stem cells in an embryo important?

Because they have the potential for regeneration of damaged cells

An organisms niche is (A) The range of physical and biological conditions in which an organism lives and the way in which it uses those conditions.
 Technically, any of the answers could be true, however, A is the only one that offers a broad definition.A niche is not only the location and conditions in which an organism lives, but also the organisms role within that niche and how it uses the resources to survive.