Choose the correct option. The total water

As far as we are aware, water covers 71% of the earth's surface. The oceans, rivers, lakes, ice caps, groundwater, and atmosphere all contain a large portion of the total amount of water on earth. Water in lakes, rivers, seas, oceans, and groundwater do not remain constant, although the overall amount of water on Earth does.

So the answer is (iv) of the world remains constant.