What method do researchers use when they need to exert significant control over what happens in their study

Which was an effect of the nuclear disaster at chernobyl, ukraine? people and animals did not get sick. drinking water was unsafe for a long time. forests got healthier than they had been. all the nuclear power plants in the world were closed.

What was the midwest states often called because they were located in the center of the nation

The two-factor theory of emotion was proposed by