Final Answer:
The development that best supports Stevens' claim about African American suffrage in the last paragraph of the excerpt is option A, the passage of the Fifteenth Amendment to the U.S. Constitution.
Step-by-step explanation:
The Fifteenth Amendment, ratified in 1870, explicitly prohibited the denial of voting rights based on race or color. This aligns with Stevens' claim about African American suffrage, as it legally granted African American men the right to vote, marking a significant step toward political inclusion.
The Thirteenth Amendment, while crucial for abolishing slavery, did not directly address voting rights. Ulysses S. Grant's presidency (option B) was notable but not inherently linked to African American suffrage. The Civil Rights Act of 1875 (option D) aimed to prevent discrimination in public facilities but did not focus on voting rights.
The Fifteenth Amendment, therefore, stands out as the pivotal development supporting Stevens' claim. By acknowledging the importance of this amendment, one can substantiate the assertion that legal measures were taken to ensure African Americans' right to vote, a central theme in Stevens' argument.