Final answer:
Radical Republicans were instrumental during Reconstruction, focusing on federal involvement to protect freedmen's rights and involving Congress in the process of readmitting former Confederate states to the Union. The correct answer that aligns with their beliefs is that the rights of freedmen had to be protected.
Step-by-step explanation:
The Radical Republicans were key figures in American History, especially during the Reconstruction era following the Civil War. Their beliefs centered on ensuring that federal measures were taken to reconstruct the South in a way that protected the rights and welfare of freed slaves. One of the core tenets of Radical Republicanism was the belief that Congress should have a significant role in the Reconstruction process. They were determined to impose strict conditions on the readmission of former Confederate states to the Union and advocated for measures to safeguard the rights of freedmen.
Looking at the provided options, the most closely related answer to the Radical Republicans' beliefs is that the rights of freedmen in the South had to be protected (Option B). They vehemently opposed a quick, lenient reintroduction of the former Confederate states without guarantees for the newly emancipated Black population. The ideology of the Radical Republicans greatly contributed to the creation of the legislation during Reconstruction that aimed to transform Southern society.