When you perform a experiment to test your hypothesis (your educated guess on what you think will happen) you complete trials to find data that is reliable and valid so you are only getting the best possible results. After you complete the experiment you write your conclusion which is when you take the data and you say if the data supported your hypothesis, if you did guess correctly at the beginning of the experiment. Which means the answer is option C "the conclusions tell why the data support or reject the hypothesis."
