Answer the following question given this paragraph: 

A scuba diver, like the one in Figure below , releases air bubbles when he breathes under water. As he gets closer to the surface of the water, the air bubbles get bigger. Boyle’s law explains why. The pressure of the water decreases as the diver gets closer to the surface. Because the bubbles are under less pressure, they increase in volume even though the amount of gas in the bubbles remains the same.


Q: A diver's air bubbles increase in size as he approaches the surface because what decreases?


A:
water pressure