Final answer:
In 1892, the Populist Party, or the People's Party, called for a graduated income tax as part of their platform to support farmers and the working class, rather than a gold-based currency.
Step-by-step explanation:
The Populist Party's Agenda in 1892
In 1892, the People's Party, known as the Populists, called for several progressive reforms, one of which was a graduated income tax. The Populists' platform was designed to support the needs of farmers and the working class amid economic hardships. Specifically, they sought reforms that would alleviate the financial strain on these groups, such as a graduated income tax, direct election of U.S. Senators, and the unlimited coinage of silver to increase the money supply and aid debt-ridden farmers.
However, the Populists did not advocate gold-based currency, as they supported the use of silver in addition to gold for backing currency, a stance that was part of their broader monetary policy agendas, like the silver standard they hoped would be brought about by their backing of William Jennings Bryan during the 1896 presidential election.
Therefore, the correct answer to the question of what the Populists called for in 1892 is c. a graduated income tax.