What noticeable trend from this graph might be used to make a conclusion?

a. average plant height is halved every time the concentration of
sodium phosphate is doubled until all of the sodium phosphate
has been used up.

b. average plant height causes an increase in the concentration of
sodium phosphate,

c. average plant height increases with an increase in the
concentration of sodium phosphate until the plants reach a
maximum possible height.

d. average plant height is not affected by the concentration of
sodium phosphate,