Final answer:
While Earth has about 366 billion billion gallons of water, much of it is saltwater. Only 2.5% is freshwater, and the majority of that is not easily accessible. There's not enough information to accurately answer the multiple-choice question about gallons of water per person.
Step-by-step explanation:
The Earth is indeed vast and covered with a significant amount of water. However, when we consider the amount of water that is actually usable to humans, the figure is much smaller than we might initially think. The Earth has around 366 billion billion gallons of water. But, most of this water is not freshwater; it's salt water contained in the oceans. Only about 2.5% of the Earth's water is freshwater, which is necessary for human consumption and agriculture, among other uses.
Furthermore, the majority of this freshwater is locked up in glaciers and ice caps or held underground, with a very small percentage being accessible surface water. This underscores the importance of water conservation, as the demand for freshwater for drinking, agriculture, and industrial uses far exceeds the readily available supply. Now, to calculate the amount of water per person, we would divide the total gallons of water by the current global population. However, since we lack the exact recent population figure here, it is not possible to provide a precise answer to the multiple-choice question presented.