In an appropriately designed experiment, a scientist is able to test the effect of:

A) a single variable

B) multiple variables

C) the hypothesis

D) scientific observations

A) a single variable

Explanation:

An appropriately designed experiment usually involves only one independent variable. This allows the scientist to truly determine whether the variable manipulated is what had an effect on the subject. You may test more than one variable, but this is usually done or experimented separately, or one at a time.