Holly has planted a garden in her backyard, but the garden will not grow. after doing some research, holly has constructed a hypothesis. she thinks her garden will not grow because the soil does not have enough potassium. holly adds potassium to the soil around half of her plants and does nothing to the remaining half. her hypothesis seems to be supported. the plants with additional potassium grew taller and fuller than the plants without potassium. which of these steps of the scientific method should she take next?