An experiment in which only one variable is changed is a (an) experiment.

Answer;

D. controlled

An experiment in which only one variable is changed is a controlled experiment.

Explanation;

-A control experiment is an experiment where the researcher only changes one variable at a time in order to isolate the results.

In a controlled experiment, most conditions are constrained so that they do not change. One or two other conditions are then changed and measured by the experimenter. These are known as the independent variables.

For example; An experiment where all subjects involved in the experiment are treated exactly the same except for one deviation.

the electromagnetic energy from the sun arrives in the form of visible and invisible light.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.