a student conducted an experiment to test whether talking to plants would help them grow faster. he set up the following two groups: group 1: spoken to and hand watered. group 2: not spoken to and then watered with sprinklers. after three weeks, the plants in group 1 showed much mote growth than those in group 2. based on the results of this experiment, which is the best conclusion? A: they are not valid because the student ran a controlled experiment B: they are not valid because the student did not control all the variables that can affect plant growth C: they are valid because the dependent variable caused a change in the independent variable D: they are not valid because the time frame to grow a plant is too short