Answer: B) not all cultures define incest the same way.
Explanation: Incest taboo is the rule based on culture that declines or restricts closely related individuals to make any intimate or sexual relation .This taboo is seen differently among various cultures because other culture might permit making such relations or have no objection related with this situation.
Other options are not appropriate because most cultures has the information of incest and neither they have changed it with levirate. Cultural has different taboos on different subjects and incest is not encouraged by cultures.
Thus, the correct option is option(B).