Microbiologically induced corrosion is largely independent of the:

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.