Which Experimental Observation Contributed to a Better Understanding of Translocation

Which experimental observation contributed to a better understanding of translocation in the phloem?

A) Positive pressure in the xylem forced liquid out of cut aphid stylets.
B) Positive pressure in the phloem forced liquid out of cut aphid stylets.
C) Negative pressure in the xylem drew liquid in from cut aphid stylets.
D) Negative pressure in the phloem drew liquid in from cut aphid stylets.
E) Positive pressure in the xylem drew liquid in from cut aphid stylets.