A toxicologist is interested in examining the effects of a new fungicide on controlling the presence of early-blight in potato crops in southern Alberta.

He randomly selects 10 potato crops to be treated with the new fungicide and 10 potatoes fields to be left untreated. To toxicologist then estimates the average number of plants affect by early-blight on each field.

In this research, which best describes the variable "field treated with new fungicide or not"?

a. an explanatory or independent variable

b. a bivariate variable

c. a descriptive variable

d. a categorial variable

e. a response or dependent variable

f. none of the above