Final answer:
The word 'prosperous' in the context of the passage suggests success and growth, therefore the best meaning is (b) Flourishing.
Step-by-step explanation:
The best meaning for the word prosperous in the context of the selection from What Caused the Dust Bowl is (b) Flourishing. Context clues within the passage indicate that prior to the 1930s, there was a period of success and growth, suggesting that 'prosperous' refers to a state of being successful and economically healthy. This interpretation is confirmed by the historical context of the Dust Bowl, wherein the region previously experienced agricultural success before the devastating events of the 1930s.