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D. All variables are measured to provide data for the experimental results

Explanation:

In an experiment, variables are changed from one part of the experiment to another to see the change in effect so option A is incorrect.

Not all variables are changed in experiments. Only independent variables are changed so that their differential effects on the dependent variable is measured. Option B is therefore incorrect.

Not all variables affect the results o the experiment so option C is incorrect as well.

Variables are indeed measured so that data is produced for the results which would enable conclusions to be made so option D is correct.

69 is the correct math for the amino acids

answer; ///animal spirits;