Reporter Genes Such as Those for Green Fluorescent Protein (GFP)

Reporter genes such as those for green fluorescent protein (GFP) are found on many commercial plasmids. These genes are useful to determine:

A) if the plasmid is in the host.
B) if a gene is present in a library.
C) if a foreign protein is being expressed on a vector.
D) the relative strength of a promoter sequence.
E) all of the above.