Two scientists are studying how different soils affect tree growth. The scientists take care to use exactly the same procedures to carry out their investigation. The results of the two scientists' test results are similar, but not identical. What is the most likely cause of these differences? A. The scientists are probably not performing the tests correctly because results from the same scientific experiment should always be identical. B. The scientists probably did have identical results, but one of the scientists made a mistake when recording the data. C. Most living things are different from each other, so they may respond slightly differently in investigations. D. Scientific investigations are never carefully controlled, so they will always produce different results.