Testosterone is an example of a chemical signal that affects the very cells that synthesize it, the neighboring cells in the testis, along with distant cells outside the gonads. Thus, testosterone is an example of
A) an autocrine signal.
B) a paracrine signal.
C) an endocrine signal.
D) both an autocrine signal and a paracrine signal.
E) an autocrine signal, a paracrine signal, and an endocrine signal.
