Final answer:
De Beers combated revenue decline during the recession by reducing diamond production, focusing on marketing and promoting the emotional value of diamonds as an investment, and expanding their distribution network.
Step-by-step explanation:
During the recession, De Beers combated revenue decline by implementing several strategies. One of the main strategies was reducing diamond production to create artificial scarcity and drive up prices. They also focused on marketing and promoting the emotional value of diamonds as an investment option, targeting affluent consumers. Additionally, De Beers expanded their distribution network to new markets, such as China, to tap into growing consumer demand.