Bacteria cells can be used to produce insulin for the treatment of diabetes in humans. Which best explains how the bacteria cells are able to produce insulin for humans?

A. The bacteria have been grown on a petri dish containing insulin.

B. The bacteria have been genetically engineered to contain the DNA needed to produce insulin.

C. The bacteria have been exposed to radioactivity to create mutant strains capable of producing insulin.

D. The bacteria have been grown on a petri dish containing sugar; the bacteria produce insulin in response to the sugar.