Why Are Genetic Researchers Not Worried About the Bacteria E

Why are genetic researchers not worried about the bacteria E. coli escaping into the natural environment?

A) E. coli is a harmless bacteria outside the human intestine.
B) The research strain of E. coli bacteria is dependent on a laboratory environment to survive.
C) Researchers have developed an antibiotic spray for any and all possible E. coli mutations.
D) Laboratory researchers have a triple fail-safe protocol for containing E. coli bacteria.
E) E. coli has a gene that causes it to be sterile in a natural environment.