A child fills a pail by using a water hose. After finishing, the child plays in a sandbox for a while before tipping the pail over to empty it. If gives the volume of the water in the pail at time , then the figure below shows as a function of .

graph of a function that is zero for t between 0 and 3, then increases linearly to y=1 as t increases to 4, is constant at y=1 until t=8, then decreases linearly to y=0 as t increases to 9. it continues at y=0 until t=14, then decreases linearly to y=-2 as t increases to t=15, is constant at y=-2 until t=17, then increases to y=0 as t goes to t=18, and is zero for t between 18 and 20.

At what time does the child:
A. Begin to fill the pail?
B. Finish filling the pail?
C. Tip the pail over?

(What would the graph of look like if the child filled the pail by using a play shovel to repeatedly scoop water from a larger bucket and dump it in the pail instead of using a hose?)

You can earn partial credit on this problem.