Mark: I'm really worried about the heavy rainfall we've had for the past three days. I predict a major flood in the low-lying areas by tomorrow morning.
Sarah: Why do you think so, Mark? What makes you so sure?
Mark: Well, the ground is completely saturated, and the river has already overflowed its banks in several spots upstream. If it continues like this, the water has nowhere else to go but into the towns.
Which of the following best supports Mark's prediction about a flood?
A) The weather forecast predicts sunny skies for the next week.
B) People in the low-lying areas have already started evacuating.
C) The river levels are rising, and the ground cannot absorb more water.
D) There hasn't been any significant rainfall in the region for months.