placebos are used in experiments to group of answer choices control for the variability of individuals who tend to volunteer for research studies. control for the expectations of some research participants that they will improve just because they are in a research study. determine whether an independent variable actually causes a statistically significant change in a dependent variable. make certain that the treatment and control group are randomly selected.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

the three components of a nucleotide are the nitrogenous base, the phosphate group and the five-carbon sugar.

the titanic would be the correct answer

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