Which statement about controlled experiments is true? a) in a controlled experiment, all variables must be kept the same b) controlled experiments cannot be conducted on living things c) a controlled experiment only tests one variable at a time d) scientists always utilize controlled experiments

The answer is

C) A controlled experiment only tests one variable at a time

false because ozone (o3) depletion does not cause global warming, but both of these environmental problems have a common cause: human activities that release pollutants into the atmosphere altering it.

global warming is caused primarily by putting too much carbon dioxide into the atmosphere when coal, oil, and natural gas are burned to generate electricity or to run our cars.

explanation: