3+ -t X A pump allows water to flow into a tank at the rate of r (t) = 3t liters per minute, where t is the time in minutes since the pump was turned on. Which of the following defines a function that measures the accumulation of water in the tank during the time period from t = 1 tot = x as the variable x moves along the t-axis as shown in the figure above? A f ( 2) = 320 B f (20) = 1+ 3x C f(x) = 3tdt