One of the Problems with Plasmids Like PUR278 Is That

One of the problems with plasmids like pUR278 is that there is no true marker for determining whether or not the plasmid contains the inserted gene since the cloning site does not lie within any specific gene. Which of the following would be an extremely useful tool for rapid selection of those bacteria that have taken up a plasmid with the desired DNA insert?

A) look for the production of the lacZ gene by adding X-gal to the growth medium
B) include the gene for a fluorescent protein such as GFP in the inserted DNA
C) after ligating the DNA insert and plasmid, separate the mixture of DNA molecules by agarose gel electrophoresis to isolate the DNA molecule that corresponds to the size of the plasmid+insert
D) look for ampicillin resistance in the transformed cells
E) none of the above would be effective