Question

why did yield vary among replicates receiving the same treatment? a) organisms among replicates differ genetically b) yields were measured with some degree of error c) treatments were established with some degree of error d) all of these factors could have contributed to the variation in yield

Explanation:

Genetic differences among organisms can affect yield. Measurement errors can also lead to variation in reported yields. Errors in establishing treatments can impact the actual treatment received by replicates, thus affecting yield. So all these factors can contribute.

Answer:

d) All of these factors could have contributed to the variation in yield