A scientist was asked to test the effect of a new vitamin for rats. His hypothesis was that young rats that had vitamins added to their food would gain weight faster than young rats fed a normal diet. He predicted that if young rats were fed vitamins, then they would gain more weight by the end of the experiment. He tested the effect of adding vitamins to some of the rats' diet by measuring the amount of weight each rat gained after three months. He then determined the average weight gained in each group. To analyze his results, he put the data he collected into the table shown below. How was or wasn't the scientific method followed in this experiment?

A. The scientific method was followed because there was an experimental group and a control group.

B. The scientific method was not followed because the experiment was not repeated many times by many different people.

C. The scientific method was not followed because the scientist did not write down the question to be tested.

D. The scientific method was followed because the experiment tested the hypothesis and produced reliable results.