A citrus farmer wants to know which of three fertilizers (A, B, and C) is most effective for increasing the number of oranges on his trees. He is willing to use 30 mature trees of various sizes from his orchard in an experiment with a randomized block design.

a. Describe a randomized block design for this experiment. Justify your choice of blocks.

b. Explain why a randomized block design might be preferable to a completely randomized design for this experiment.