Final answer:
Biofilms are complex and dynamic ecosystems that form on various surfaces, including water distribution systems. They are highly structured communities that can harbor opportunistic pathogens and contain grazing protists that consume bacteria.
Step-by-step explanation:
Biofilms are complex and dynamic ecosystems composed of microorganisms that form on various surfaces, including water distribution systems.
They are highly structured communities that provide a selective advantage to their constituent microorganisms.
Biofilms have the potential to harbor opportunistic pathogens and also contain numerous grazing protists that consume bacteria.
Therefore, the correct answer is option D) biofilms that may harbor opportunistic pathogens and numerous grazing protists that consume bacteria.