During a controlled experiment, a scientist isolates and tests
a. a conclusion.
b. a mass of information.
c. a control group.
d. a single variable

During a controlled experiment, a scientist isolates and tests D. a single variable. An experiment is considered controlled or fair if variables that may affect the outcome are kept the same or controlled and only the independent variable is changed.

A. a conclusion - FALSE

The conclusion is the outcome or result of the experiment. It states whether the hypothesis or objective of the investigation is supported by the data or not.

B. a mass of information - FALSE

A mass of information is reviewed and used either as a basis for the hypothesis or to explain the data and results of an experiment.

C. a control group - FALSE

The subjects or samples of an experiment may be grouped into the control group and the experimental group. The experimental group is the group wherein the changes in the independent variables are administered. The  control group serves as a baseline to see whether the independent variables are affecting the outcome of the experiment. It usually is the group that does not receive the treatment or intervention in the independent variables: they receive the standard value or nothing. If the treatment or independent variable is known to produce results, a positive control may be used. The positive control group shows the results when the independent variable definitely affects the outcome. The opposite is called the negative control group which shows the outcome when the independent variable has no effect on the outcome.

D. a single variable - TRUE.

A fair and controlled test ensures that all other factors that might affect the outcome of the investigation are held constant. This is so that it is clear and certain that only the independent variable is affecting the outcome and not some other factors.

Keywords: controlled experiment, fair testing

it is a. i hope this .