Given a scientific question, generate a correct answer to it.

[Q]: A mixture of a metal with one or more other elements is called?
[A]: an alloy

[Q]: The arid environment of a desert, for instance, can quickly deplete an animal of what?
[A]: water

[Q]: Each endocrine hormone affects only certain "target" cells, which have molecules of what on the surface that enable binding of a given hormone?
[A]:
protein