Which pair of elements can be used to determine the age of a fossil that is over one billion years old?
lead, which is radioactive, and uranium, which is stable
carbon, which is radioactive, and nitrogen, which is stable
argon, which is radioactive, and lead, which is stable
potassium, which is radioactive, and argon, which is stable

Embryonic stem cells are cells derived from an embryo. these cells can be used to create new tissues for patients suffering from certain illnesses and disorders. which statement best summarizes why the use of embryonic stem cells could be seen as unethical? a. some people consider embryos to possess rights equal to those of fully developed human beings. b. extracting stem cells from embryos is a very energy-intensive process, which consumes resources that could be used elsewhere. c. embryos are difficult to obtain, so the monetary cost of using them for research outweighs their benefit. d. the process of extracting stem cells from embryos generates biohazardous waste that cannot be safely disposed of.