A crop scientist is conducting research with a drought resistant corn hybrid. She is interested in determining if increasing the spacing between these plants will increase yield. She prepares 30 single acre plots and randomly assigns 15 to have normal spacing while the other 15 are planted with an expanded spacing. The resulting average yield for each group of 15 plots was recorded. Select all that apply.

Select one or more:
a. The explanatory variable is whether the corn plants had normal spacing or expanded spacing.
b. The response variable is the yield of the crops.
c. The explanatory variable is the yield of the crops.
d. The response variable is whether the corn plants had normal spacing or expanded spacing.
e. This study is best described as an experiment.
f. This is best described as an observational study.