The correct answer is option 'D' - Pittsburgh region.

Explanation:
The 'Rust Bowl' of the USA is associated with the Pittsburgh region. This term refers to a region in the United States that was once a major industrial and manufacturing center but experienced a decline in the late 20th century.

Key points:
1. Industrial and manufacturing center: The Rust Bowl region, also known as the Rust Belt, was historically a hub of industrial and manufacturing activity. It was home to numerous steel mills, factories, and other manufacturing facilities.
2. Economic decline: However, starting in the 1970s, the region began to suffer from economic decline. Many factors contributed to this decline, including increased competition from foreign manufacturers, the outsourcing of jobs, and changes in the global economy.
3. Impact on Pittsburgh: Pittsburgh, located in western Pennsylvania, was one of the major cities in the Rust Bowl region. It was known as the "Steel City" due to its prominent steel industry. When the steel industry declined, Pittsburgh faced significant economic challenges.
4. High unemployment: As the steel mills and other manufacturing facilities closed down or downsized, thousands of workers lost their jobs. The region experienced high unemployment rates and struggled to transition to other industries.
5. Revitalization efforts: In recent years, there have been efforts to revitalize the Rust Bowl region and diversify its economy. Pittsburgh, in particular, has seen a resurgence in sectors such as technology, healthcare, and education. The city has transformed into a center for innovation and entrepreneurship.
6. Cultural significance: The term "Rust Bowl" not only describes the economic decline but also reflects the impact on the communities and culture of the region. It symbolizes the challenges faced by former industrial towns and the resilience of the people living there.

In conclusion, the 'Rust Bowl' of the USA is associated with the Pittsburgh region, which was once a major industrial and manufacturing center but experienced economic decline in the late 20th century.