The rate at which water is entering a reservoir is given for time greater than zero in the graph. A negative rate means that water is leaving the reservoir. On which interval is the volume of water in the reservoir increasing the fastest?

A (1, 5.5)
B (3, 3.5)
C (3.5, 5.5)
D (5.5, 8.5)
E (8.5, 10)