A crop scientist is conducting research with a drought-resistant corn hybrid. She is interested in determining if using fertilizer X will increase yield. She prepares 28 single acre plots and randomly assigns 14 to have normal soil while the other 14 are planted with fertilizer X. The resulting average yield for each group of 14 plots was recorded. What is the explanatory variable in this study?
1) The average yield for each group of 14 plots.
2) Whether the corn plants had fertilizer X or not.
3) This is best described as an observational study.
4) This study is best described as an experiment.
5) The response variable is the average yield for each group of 14 plots.