At one time, scientists classified all organisms into two main categories — plants and animals. Using this system, plants, such as maple trees, and fungi, such as mushrooms, were grouped together. Plants and fungi are now classified in different categories or kingdoms. What is one reason for this change? A. Plants are unicellular. B. Fungi are unable to perform photosynthesis. C. Plants are unable to perform cellular respiration. D. Fungi are autotrophic.