Answer: C) The 85-degree class.
Explanation: An experimental group simply refers to the participants who are subjected to the actual treatment during a study. In the scenario above, the groups of participants are involved, while the first group were subjected to seventy degree temperature, which corresponds to the normal oom temperature, this means they weren't subjected to any actual treatment. The other group however witnessed a temperature higher than the normal at 85 degrees and as such makes them the experimental group.