G does not have any input so it wont get any water. It is "supplied" only by D, but you can see that D's supply tube is actually blocked. There is more than one blocked tube in the picture, in fact.
H has no input either as the supply line is also blocked. Correct answer is F
Input from bottom fill, prioritised by head pressure from, Oh shit, Hs inlet is blocked also. Comes back to F. I stand corrected by the tricks in the drawing. Real mind bender.