The question is testing the understanding of synonyms, specifically for the word 'flood'. The correct answer is C because 'deluge' is another term for a flood, indicating a great quantity of water. Option A is incorrect because 'drought' means a lack of water, the opposite of a flood. Option B is wrong because a 'tsunami' is a large wave usually caused by an underwater earthquake, not synonymous with 'flood'. Option D is incorrect because 'evaporation' is the process of water turning into vapor, which is not related to the concept of a flood.