A Researcher Has Manipulated Only One Independent Variable at Two

Multiple Choice

A researcher has manipulated only one independent variable at two levels,has held constant as many other variables as possible and has balanced individual differences by using random assignment.The researcher is likely to be able to claim that the independent variable caused the observed changes in the dependent variable because the experiment is

A) internally valid.
B) externally valid.
C) a meta-analysis.
D) reliable.