Respuesta :
The only independent variable in this experiment is the amount of nitrogen Sarah uses. All of the other variables are dependent on other factor and processes, but Sarah controls the amount of nitrogen that she uses for each plant.
The correct answer is option a) Amount of Nitrogen.
The variables are the factors, which can be changed in an experiment. The variables can be of two types, dependent variable and independent variable.
The independent variables are those factors, which are independent of any changes. In this case, the amount of nitrogen Sarah administer is not dependent on any factor, so, it is an independent variable.
Whereas, the height of plant, nodules and root growth is dependent on the amount of nitrogen the plant get. SO, these are dependent variables.