Answer:
Graph D
Step-by-step explanation:
When the process starts, the water is flowing slowly, since there is only 1 valve open. That represents the part on this where the line is going almost horizontally.
When the operator opens the second valve also, then there will be more water released at once, which means that the water will come out faster, and take less time. That represents the middle part of the line, which is almost vertical.
When the operator shut's down the second valve, then the process gets slower, and that represents the part which is going slow again. And that represents the 3rd part, where the line is going almost horizontal again.
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