The Evidence That Testosterone Affects Aggressive Behavior in Humans Is

The evidence that testosterone affects aggressive behavior in humans is inconsistent. This inconsistency may be attributable to the fact that

A) testosterone's effect on human aggression not as clear as its effect on aggression in other species.
B) testosterone is very difficult to measure in humans as it is present in such miniscule quantities.
C) humans have more androgen receptors than other species do.
D) testosterone interacts with serotonin in complex ways, so it is unclear whether serotonin or testosterone is causing the aggression.