So this is the question from brilliant.org:
Which pipe (or pipes) carries water with the highest speed?
The answer given was A. I picked C, the explanation wasn't clear to me.
The pressure difference across the ends of each pipe is determined by the difference in water level between the tanks it connects. The biggest water level difference is between left and middle tanks, so water in pipe A will have the highest speed.
The pressure difference across both pipes is the same because the difference in water level is the same and it is smaller than the difference in levels between the left and center tanks. Therefore, the speed of the water is the same in both.
From which point are we measuring this pressure difference, it's really confusing how the explanation is given.