Enzymes that function inside a cell are

A. The staff giving the steroid injections did not use proper aseptic technique: Improper aseptic technique at a single clinic could cause local infections, but widespread cases across the U.S. point to a source affecting multiple clinics or batches rather than isolated procedure lapses.

B. The steroid was contaminated at the production plant, so all batches of that drug made at that plant were contaminated with the bacterium: Contamination during manufacture or compounding that led to distribution of contaminated batches nationwide can explain many cases across broad geographic areas and rapid onset after administration.

C. The bacterium is normally on the skin of people, so can easily access the patient's blood during the needle stick: While skin flora can cause infections after injections, Pseudomonas is primarily environmental and widespread patient infections clustered nationally are less consistent with routine skin flora transmission.

D. The needles were re-used and already contaminated before being used on the patients: Reused needles can cause outbreaks but would more likely produce clusters tied to a particular clinic or practitioner rather than many unrelated patients across the country.

A. True: Reverse transcriptase synthesizes complementary DNA (cDNA) from an RNA template, a process used by retroviruses and in molecular biology applications such as cloning eukaryotic genes.