A good business experiment to determine if a change in packaging affects the sale of a product should do which of the following to produce a reliable result.

Group of answer choices

a. Measure the level of sales to the control group and the test group before the change in packaging. (pretest)

b. Change the packaging only to the test group

c. All of 3 answers are correct

d. Measure the change in sales for the test group and the control group about 3 weeks after changing the packaging. (post test)