Which of the following (actual) research findings represents the most serious challenge to ...

Which of the following (actual) research findings represents the most serious challenge to evolutionary explanations of love and attraction?
 
  a. In areas of the world where parasitic diseases are prevalent, men and women value physical attractiveness.
  b. Women are less likely than men to admit the importance of physical attractiveness, but observations of behaviors reveal no gender differences.
  c. Men tend to prefer younger women, and women tend to prefer men of the same age.
  d. Men become more upset at sexual infidelities, and women at emotional infidelities.