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.

her next move would be to use agarose gel electrophoresis to separate the dna molecules of varying length and create a dna fingerprint.

it's d - life cycles - apex

oxygen is the first element in group 16 (via) of the periodic table. the periodic table is a chart that shows how chemical elements are related to each other. the elements in group 16 are said to belong to the chalcogen family. other elements in this group include  sulfur, selenium, tellurium,  and  polonium.  the name chalcogen comes from the greek word  chalkos,  meaning "ore." the first two members of the family, oxygen and sulfur, are found in most ores.

oxygen is by far the most abundant element in the earth's crust. nearly half of all the atoms in the earth are oxygen atoms. oxygen also makes up about one-fifth of the earth's atmosphere. nearly 90 percent of the weight of the oceans is due to oxygen. in addition, oxygen is thought to be the third most abundant element in the universe and in the solar system.