The most critical defining characteristic of a true experiment is often seen to be a high degree of control over the
a. arrangement of experimental conditions.
b. choice of dependent variables.
c. random assignment of participants to experimental conditions.
d. systematic manipulation of independent variables.

Option (c) is correct.

From the given options, the most decisive peculiarity of a true experiment is given as follow: "generally seen to be a high rate of control over a random assignment of individuals to experimental circumstances.

Thus the correct option in this particular case is (C).

it apply by theyre artifacts

hygrometers and hair thermometers (often found as part of hygrometers/psychrometers) can be used to measure humidity. barometers are used to measure atmospheric pressure, while anemometers are used to measure wind speed. so the 2nd and 4th choices should be the correct answers.