The true statement about the impact of the cotton gin and railroads on westward expansion is:
B) The cotton gin made cotton processing faster, fueling the expansion of slavery to new lands in the South and West. Railroads opened up faster transportation routes to these areas.
This statement accurately reflects how the invention of the cotton gin significantly increased the demand for cotton production, leading to the expansion of slavery into new territories, while railroads provided crucial infrastructure for transporting cotton and other goods, facilitating westward movement.