Although they appear to be in top physical condition, professional basketball players often get sick ...

Although they appear to be in top physical condition, professional basketball players often get sick during the eighty-two-game, six-month-long NBA season. According to the textbook, a likely reason is that ____.
 
  a. they are exposed to many more germs than other people
  b. their bodies' reserves of adaptive energy are worn down by the constant and long-lasting stressors of the season
  c. a physical defense mechanism kicks in to protect the athletes from burnout
  d. their sympathetic nervous systems become overworked in the resistance stage, and too few catecholamines are released into the bloodstream