From API RP 571 on Microbiologically Influenced Corrosion (MIC):
"MIC depends on the presence of water, nutrients, and specific microbial species such as SRB (sulfate- reducing bacteria)."
"While flow velocity may influence deposition and oxygen content, MIC can occur in both stagnant and flowing systems. Hence, it's not strongly dependent on velocity." Thus, option D is correct - MIC is largely independent of flow velocity.