The correct answer to this question is A, 0.25%. Most experts round up the amount to .3%, which is what .25 rounds up to. This amount is low, considering that 71% of the Earth's surface is covered with water. Icecaps, soil, and glaciers use the other 99.7%. Most of the .3% is still unattainable for human usage.
Most of the water we use as humans come from rivers, which is a surface water. There is also groundwater than humans can use. The underground water is used as moisture for soil. It is also the reason why rivers flow because they keep streams going.