4) About 20 years ago, money was invested to create a forest by planting trees in an open field. Researchers want to check on the progress of the trees. However, there are way too many trees to examine each one. Therefore, it is desired to take a random sample. a) Although it would be convenient and easy, it is not a good idea to just sample the first 50 trees the researcher walks up to and sees. Why not? b) Describe how to carry out a cluster sample. c) What would be easier: a cluster sample or simple random sample? Why?.