Final answer:
The main economic sources of San Bernardino County, California, include agriculture, tourism, and the high-tech industry.
Step-by-step explanation:
The main economic sources of San Bernardino County, California, are diverse and include agriculture, tourism, and the high-tech industry. Agriculture plays a significant role in the county's economy, with crops such as dairy products, livestock, and viticulture contributing to its agricultural base. Tourism is also important, with the county attracting millions of tourists each year. Additionally, the high-tech industry, particularly in the Silicon Valley region, is a major source of economic activity in the county.