Normal sexual behavior is that which
a. reflects the average or median behavior of a group
b. is supported by religious teachings
c. reflects the preferences of those of high status in a society
d. leads to successful reproduction

a. Represents the average or median behaviour of a group.

Explanation:

Any 'normal' behaviour denotes the usual aspects of the variable/ attribute, as represented by average for a group of people.

Examples : Normal Heart Beat - 70 to 80  is a range decided around average after examining various people's heart beat.

Similarly, Normal Sexual Behaviour is average behaviour attributed after evaluating sexual behaviour of various people.

i believe the answer is: returns on investments, no wages

people who belong in upper class society would most likely get there by obtaining multiple source of income, which a certain percentage of ownership for businesses. since most of them are job creator, they would most likely get their money from profit, not wages.