A new product is designed to make plants grow faster. Twenty plants are fed the new product and twenty plants are used as a control group. Which possible issue might cause an unavoidable error in the study? A) Plants of different species grow at different rates. B) Plants that are given more water or sunlight will grow faster than others. C) The plants used were at different ages and therefore might grow at different rates. D) Some plants will naturally grow faster or slower than others plant of the same species.