Farmer Brown tests the hypothesis that the more alfalfa sprouts cattle eat, the more milk they produce. He divides his pasture into four fields and puts twenty cattle in each field. Field 1 cows get no alfalfa sprouts, field 2 cows get ten pounds of sprouts per day, field 3 cows get twenty pounds of sprouts, and field 4 cows get thirty pounds. He feeds all groups fifty pounds of regular hay per day, uses the same breed of cattle, and gives them the same amount of water. He measures gallons of milk produced per cow every day. What is the independent (tested) variable in Farmer Brown's experiment?A)The ratio of hay to milk produced. B)The number of cattle in each field. C)The amount of milk the cows produce. D)The amount of alfalfa sprouts the cattle are fed.