There are several properties of water that make earth a suitable environment for life, including water's high boiling point and high heat capacity. which best explains why this characteristic of water is important for marine life?
a.) it allows water to remain in its liquid form even at relatively high temperatures.
b.) it allows water to vaporize easily, powering the water cycle.
c.) it allows water to be denser, making it easy for living organisms to move through.
d.) it allows water to resist freezing and thawing cycles.

D.) It allows water to resist freezing and thawing cycles.

The ability of the water molecule to absorb and retain heat is called as heat capacity of water, because of this property the temperature of water remains the same for long, irrespective of the external environment. It allows water to resist freezing and thawing cycles because water molecules will resist change in it's temperature. This temperature regulation will prevent instant heating and cooling, hence, will provide suitable environment for the survival of marine organisms.  

b is the correct answer