Scientists are studying fertilizers to help grass grow in southern California. Fertilizer is any substance that can be added to soil to help plants grow in it. In other words, fertilizer makes soil more fertile. The scientists set up different plots of land that all use the same type of soil, but they use different types of fertilizer in each plot. Scientists then measure the grass growth in the different soils over time.

How should scientists set up the control group in this experiment?
A. a plot with grass but no fertilizer in the soil
B. a plot with grass and many types of fertilizer in the soil
C. a plot without any grass or any fertilizer in the soil
D. a plot without any grass but with fertilizer in the soil

A scientific experiment contains two types of groups: the control and the experimental groups. The control group in any scientific experiment is the sample which does not receive the variable we need to test which is provided in the experimental groups.

In the given question, the scientist wanted to study the effect of fertilizers on the growth of the grass. so the parameter (variable) to be studied is fertilizer. The experimental samples are provided with different concentration of the fertilizer but the control sample will not receive the fertilizers as the control sample provides the base or reference to the experimental group to increase the accuracy of the results obtained.

Thus, option-A is the correct answer.