Final answer:
The C. Republican Party was supported most by farmers and merchants.
Step-by-step explanation:
The party that was supported most by farmers and merchants was the Republican Party. In the late 18th and early 19th centuries, Republicans attracted wealthy landowners tied to plantation-based slavery as well as ordinary farmers who wanted to see the economy remain tied to agriculture and less prosperous merchants who wanted to challenge the control of entrenched leaders.
Republicans were strongest in the South, as well as the western areas of Pennsylvania and New York. Thus, the party in the United States found support among farmers and merchants. This base was typically drawn from the party's advocacy for protective tariffs, which benefited farmers, and its alignment with business interests and industrial development in the post-Civil War era.