To modify the Constitution, an amendment must first be proposed by:

The correct answer is C. Congress or the states.

To modify the Constitution, an amendment can be proposed either by a two-thirds vote in both the House of Representatives and the Senate (Congress) or by a constitutional convention called for by two-thirds of state legislatures. This process ensures that any changes have substantial support either at the federal or state level. If you have more questions or need further assistance, feel free to ask!