C because...
Models represent objects, events, and processes in the real world.
Models are often used when an object, event, or process
occurs too slowly or too quickly;
is too small or too large;
is too complicated or too dangerous.
The ocean is spreading at such a slow rate that it would take scientists 50 or more years to collect enough meaningful data from the ocean floor to complete a study. Therefore, scientists use models in order to both predict how the floor will keep spreading and to understand what the ocean floor looked like thousands of years in the past.