Scientists Measured the Pressure in the Xylem of Redwood Trees

Scientists measured the pressure in the xylem of redwood trees at different heights and found that the higher they made their measurements,the lower the pressure.They extrapolated this to a pressure of zero,and concluded that the tallest a tree could grow is 122-130 meters.The tallest known tree on Earth is 112.7 meters.What assumption were the scientists making to conclude that when pressure was zero the plant could grow no further?

A) Any leaves above that point would not receive sunlight.
B) Any leaves above that point would not receive water.
C) Stems above that point could not transport sugars in their xylem.
D) Transpiration would be less than uptake of water from the xylem.
E) The osmotic pressure would be greater than gravity.