Answer:
C. The scientist's conclusion is flawed because the number of hours of sunlight changed and, therefore, the experiment is not controlled.
Step-by-step explanation:
A controlled experiment is an experiment used to test a single variable at a time. The variable that is being tested is called the independent variable, and it is directly manipulated by a scientist. The rest of the variables need to remain unchanged in order not to get wrong results like the scientist in the given scenario.
As the scientist is trying to see how gamma rays affect marigolds, only the gamma ray exposure is supposed to change throughout the experiment. The amount of water remained the same, but the number of hours of sunlight didn't. That's why we don't know what exactly affected the growth of marigolds - the sunlight or the gamma rays? And that's why the scientist's conclusion is flawed.