What happens during a controlled experiment

a. no observation are made

b. many variables are changed

c. a factor called prediction is changed

d. the results of changing independent variable are observed

what is the correct answer
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The gulf stream is a warm water current that flows away from the equator to northern europe. witch of these does it cause. a. crashes of warm and cool water in the ocean b.colder climates near the equator c.large waves on the cost of europe d.warm climates in northern europe