In contrast with research, research allows cause-and-effect conclusions.

In contrast with correlational research, experimental research allows cause-and-effect conclusions. This is because experimental research limits the number of independent variables to one variable, so we know that the independent variable has an effect on the dependent variable. In correlational research the independent variable is not limited to one, so while we know there is a correlation between the independent and dependent variable, we don't know that it caused it. An example is that on a rainy day we see a people carrying umbrellas. However, the correlation between people carrying umbrellas and the rain does not mean the people carrying the umbrellas caused the rain.

It’s either d or b ! but it might be b