Regarding how biological factors contribute to personality development, research has found that a. one's genetic makeup contributes very little to the continuity of personality. b. extraversion is associated with high levels of the stress hormone cortisol and to the responses of the amygdala of the brain. c. neuroticism is associated with high levels of the neurotransmitter dopamine. d. the nervous system deterioration associated with Huntington's disease or Alzheimer's disease can cause affected individuals to become moody, irritable, and irresponsible