Based on what you know about natural selection, which of the following must be true if evolution is the explanation for what the grants have observed over time on daphne? select all that apply.

food must be plentiful for all birds.
beak depth and length must be heritable.
beak depth and length must show variation among individuals of a single species.
beak depth and length must affect survival and/or reproduction of birds.
over time, individuals can evolve to better fit the environment by changing heritable traits.
the beaks of individual birds can change depending on what food is available.

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.