Final answer:
The correct synonym for 'proceed CAREFULLY in unknown waters' is 'Navigate cautiously in unknown waters'.
Step-by-step explanation:
The synonym for "proceed CAREFULLY in unknown waters" is C) Navigate cautiously in unknown waters. The word 'cautiously' is similar in meaning to 'carefully,' and both suggest taking actions with a high degree of attention to avoid risk or errors, especially in a situation that is uncertain or unfamiliar.