Question

carmen is testing to see how four pepper plants respond to different variables. she is interested in testing several factors (different amounts of fertilizers, insecticides, water, and sunlight). in order to obtain the most reliable results, what should carmen do?
randomly test two variables on two plants.
test all the variables on each of her four plants.
test one variable at a time on three plants, while using one plant as a control.
test all the variables on one plant, two of the variables on another plant

Explanation:

In a scientific experiment, to obtain reliable results, it's best to change one variable at a time while keeping others constant. A control group is also needed for comparison. Testing one variable at a time on three plants with one plant as a control helps isolate the effects of each factor.

Answer:

Test one variable at a time on three plants, while using one plant as a control.