Question

the variable a scientist manipulates in an experiment is called the observation variable independent variable controlled variable dependent variable

Explanation:

In experimental design, the independent variable is the one that the researcher deliberately manipulates to observe its effect on the dependent variable. Observation variable is not a standard term for this concept, controlled variables are kept constant, and dependent variables are the ones being measured (not manipulated). So the variable a scientist manipulates is the independent variable.

Answer:

B. independent variable