Answer:
(b) The plots
Step-by-step explanation:
The plots are the experimental units as they are the objects subjected to the measurements. The variety of apple trees is the explanatory variable since they promote change in the experimental unit through two different treatments (Fuji or Gala variety). The farmer is the one conducting the experiment and the number of apples is the result to be analyzed. The orchard as a whole does not interfere in the experiment since each plot is being studied.