Sheila conducts an investigation to see how the amount of salt dissolved in water affects the density of the water. Which statement best describes the correct plan for her procedure?

Sheila should change the amount of salt to test its effect on density, so the amount of salt is the independent variable and density is the measured outcome. To make the test fair, she should keep the type of salt and the amount of water constant. Therefore, the type of salt and amount of water are controls, while the amount of salt and density are variables, as stated in choice C.

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