Scientists have recently discovered that certain bacteria can not only survive in extremely acidic environments, but also are thriving there, metabolizing compounds that are toxic to most other life forms.

✓ Correct Answer: Option B

The original sentence violates parallelism with 'not only... but also'. The structure requires 'can survive' to be parallel with 'can thrive'. Option B correctly uses 'thrive' to maintain parallel structure with 'survive', implying 'can' before both verbs.