Final answer:
The modern sector has an expanding Westernized middle class.
Step-by-step explanation:
The market sector that has an expanding Westernized middle class is the modern sector. As countries develop and undergo market-oriented economic reforms, their standard of living increases and their middle class expands. This is particularly true in well-developed economies like the United States, Japan, and Western Europe, where the majority of the workforce is employed in the service industry.