What is the purpose of controlling the environment when testing a hypothesis?

it allows the scientist to determine the effect of the changed variable.
it allows samples and organisms to be tested under comfortable conditions.
it makes it easier for the scientist to perform the steps of the experiment.
it ensures that the scientist is undisturbed while performing the experiment.

When testing a hypothesis, it is important to control the environment to make sure that no other unforeseen variable affect the outcome of the experiment. Therefore the answer is "It allows the scientist to determine the effect of the changed variable."

The correct answer is It allows the scientist to determine the effect of the changed variable.

Controlled environment while testing a hypothesis or while performing any experiment serves important functions:

It ensures the reproduciblity of that experiment and hence, it increases the reliability of that experiment.It increases the accuracy of the results of an experiment.It allows to determine the effects of changed or independent variable on the dependent variables. For example, if scientist is checking the effects of temperature on enzyme activity then other factors such as amount of enzyme, substrate, pH, pressure etc should be controlled as they can alter the results.