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a student conducted an experiment to test whether talking to plants would them to grow faster. the student talked to one group of plants and hand watered them. the student did not talk to the other group of plants and used sprinklers. after three weeks, the plants that were spoken to showed much more growth than the plants that were not. the student concluded that talking to plants makes them grow.

which statement describes the validity of the student's results?

a. they are valid because the student ran a controlled experiment.
b. they are not valid because the student did not control all the variables that can affect plant growth
c. they are valid because the dependent variable caused a change in the independent variable
d. they are not valid because the time frame to grow a plant is too short.