In the field experiment described in the text, city library patrons were approached by a confederate in the parking lot. This experiment had two independent variables. What were they?

a. confederate's behavior and cleanliness of the parking lot
b. cleanliness of the parking lot and how the patrons disposed of the handbill
c. confederate's behavior and number of library fines
d. how patrons disposed of the handbill and number of library fines

A). Confederate's behavior and cleanliness of the parking lot.

Explanation:

Independent variable is demonstrated as the variable in a scientific experiment that could be manipulated or controlled in order to observe its impact on the dependent variable.

In the given example, the two independent variables would be the 'confederate's behavior and the cleanliness of the parking lot' as these are not dependent and could be controlled or manipulated in order to evaluate its impact on the dependent variable 'city labor patrons' in the field experiment. Therefore, option A is the correct answer.

the answer is:

c. economic output