The sphere does a dolphin swim in is the hydrosphere. The answer is letter D. The first layer, troposphere, is where we are able to do most of our activities. This is where we can see the formation of clouds, the production of rain, hail, snow and other weather phenomenon. Also, this layer is where the greatest amount of air pressure because most of the molecules of air are in this area. Like us, air has also mass and the pressure is brought down by the earth’s gravity causing an increase in weight exerted on you as you descend lower into the atmosphere. So, as you enter into the other layers of atmosphere above the troposphere, the air pressure starts to decrease. Below the atmosphere is the hydrosphere. This is where all liquid forms are located. And since the seawater has a greater mass than air, it has the greatest pressure.