During mammalian labor and delivery, the contraction of uterine muscles is enhanced by oxytocin. This is an example of
A) a negative feedback system.
B) a hormone that is involved in a positive feedback loop.
C) signal transduction immediately changing gene expression in its target cells.
D) a hormone that acts in an antagonistic way with another hormone.
E) the key role of the anterior pituitary gland in regulating uterine contraction.
Answer: B