Which Technique Allowed Researchers to Conclude That the Fibrous Proteins

Which technique allowed researchers to conclude that the fibrous proteins in sieve tube elements are normally dispersed and obstruct sieve plates only in response to cell damage?

A) Analyzing phloem sap extruded from aphid stylets
B) Freezing phloem tissue before cutting and examining it
C) Watering a plant before cutting and examining it
D) Using patch clamping to examine sieve plates
E) Exposing plants to blue light before examination