Final answer:
Cattle were crucial for Texas ranchers as a source of wealth due to eastern demand for beef, facilitated by the railroad system. In the east, cattle were valued primarily for their meat, with advancements in meatpacking lowering costs and altering the American diet. Option D is correct.
Step-by-step explanation:
Cattle were critically important to ranchers in Texas because they were a significant source of wealth, thanks to the high demand for beef in eastern markets. With millions of longhorn cattle roaming Texas after the Civil War, ranchers took advantage of the expanding railroad system to transport these cattle to eastern cities where they could be sold for considerable sums. The cattle industry was a key component of westward expansion and fundamentally shaped the economy of the Old West.
For people living in the east, cattle were mainly important as a food source. With the development of large-scale meatpacking plants in cities like Chicago and Kansas City, the cost of meat could be lowered, making beef more accessible to the American public. This transformation in the meatpacking industry also changed the American diet by making beef a staple food, further cementing the importance of Texas cattle to the eastern states.