Need help ASAP with 20 and 21

Sheila conducts an investigation to see how the amount of salt dissolved in water affects the density of the water whichstatement best describes the correct plan for her procedure? the density and the amount of water are controls, and the amount of salt and the type of salt are variablesthe amount of water and the amount of salt are controls, and the type of salt and the density are variablesthe type of salt and the amount of water are controls, and the amount of salt and the density are variablesthe type of salt and the density of water are controls, and the amount of salt and the amount of water are variableso