In humans, the organ that most directly regulates the concentration of water in the blood is the:
a) heart
b) pancreas
c) liver
d) kidney

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.

40%=2/550=1/230=3/1056=14/25