Some psychologists argue that men are more likely to take risks than females because
a. fewer men are necessary to sustain population growth in a society
b. more men generally have elevated levels of testosterone and serotonin
c. fewer men have a well-developed frontal lobe, which control impulses
d. more men have discovered that risky behavior is actually quite safe

Correct B). More men generally have elevated levels of testosterone and serotonin  

Testosterone plays an important role in the body, they are known to influence certain behaviors including aggression and dominance. They are known to affect the taking part in competitive activities and sports.  The level of testosterone and serotonin increase in the aggressive phase and it also responsible for the risk-taking behavior in males.

Both testosterone and serotonin are believed to regulate mood and social behavior.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.