Everyone knows that rivers carry freshwater into the ocean, but not everyone knows that rivers are not the oceans' only source of freshwater. Geochemist Willard Moore of the University of South Carolina has performed studies and analyses which indicate that a large volume of groundwater directly enters the seas.

performed = done
analyses = investigations
volume = amount

a. groundwater enters the ocean                     c. rivers are the ocean's only source of freshwater

b. rivers bring freshwater to the sea                d. rivers get freshwater from the oceans