A botanist is performing an experiment on two fertilizers that require different amounts of watering. She has 40 test plots, half of which are in sunny locations,
and half are in the shade. She randomly selects 10 sunny plots and 10 shady plots
for which to use one fertilizer, while the remaining plots are for the other
fertilizer, each watered differently as recommended by the manufacturer. Which
is the most important observation about this procedure? *