The answer to this question is option b. It is much harder to control variables in a field study than in an experiment.
Both of these are methods that are used to carry out investigations for research purposes.
In the field study, many variables come to play. This makes it more difficult for the researcher to control.
The experiment is carried out in a confined place probably a laboratory. This makes it easier for the scientist to control his variables compared to when it is done in the open or natural.
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