Me
select the sets that are not functions.
a = {(1, 2), (2, 3), (3, 4), (4, 5)}
b = {(1, 2), (2, 1), (3, 0), (4, -1)}
c = {(-1, 3), (0, 3), (1, 3), (2, 3)}
d = {(1, 1), (1, 2), (1, 3), (1, 4)}
e = {(6, 2), (7, 3), (6, -1), (5, 4)}

water molecules will move from the side of higher water concentration to the side of lower concentration until both solutions are isotonic. at this point, equilibrium is reached. in an isotonic solution, the flow of water in and out of the cell is happening at the same rate.

hope this < 3