Answer:
The correct answer is option A. "They should focus their attention on metabolic genes".
Step-by-step explanation:
Horizontal gene transfer refers to the transference of genetic material among species in contrast to the classic vertical gene transfer, which occurs between the parents and their offspring. Metabolic genes exhibit a high level of evolutionary conservation and are known for being horizontally transferred among bacteria and eukaryotic cells. Therefore, metabolic genes should be the focus of the researchers studying the possible horizontal gene transfer in the non-pathogenic bacteria.