Which of the following would lead to a decrease in the price differences between letters of John Wilkes Booth and Abraham Lincoln?

The scenario described in the question involves letters from historical figures, which are considered collectibles with prices influenced by supply and demand dynamics. A decrease in the price differences between letters of John Wilkes Booth and Abraham Lincoln indicates that the market values for these two types of letters are becoming more aligned.

When analyzing option C, an increase in demand for Lincoln letters alongside an increased supply of Booth letters can effectively reduce the price gap. The increase in demand for Lincoln letters would likely drive their price up, making them more desirable among collectors. Simultaneously, with an increase in the supply of Booth letters, the market would see more of these letters available, potentially lowering their prices if the demand does not keep up.

This dual movement points to a convergence in values: as Lincoln letters become more sought after and reflective of rising demand, Booth letters flooding the market would pressure their prices downward, narrowing the gap between the two. Collectively, these factors help realize a decrease in the price difference between the two types of letters, making this option the most plausible.