Gene fusions of a protein of interest and GFP, or its derivatives, can be used in all of the following EXCEPT

A) studying protein targeting to organelles in eukaryotic cells.
B) monitoring microbial protein movement inside infected eukaryotic cells.
C) tracking viral protein movement inside or between infected eukaryotic cells.
D) detecting interactions between microbial extracellular proteins and attachment surfaces.
E) CRISPR-Cas9.