Final answer:
Speaker A represents the attitudes of the Radical Republicans who controlled Congress during Reconstruction by emphasizing the need to punish those who supported secession. The option (A) is correct.
Step-by-step explanation:
The speaker who represents the attitudes of the Radical Republicans who controlled Congress during Reconstruction is Speaker A: 'Secession from the Union caused this war, and all those who supported it must now be punished.'
This speaker reflects the Radical Republicans' belief that the Southern states needed to face consequences for their secession from the Union. They wanted to punish those who supported secession and ensure that the Unionists had control in the process of reconstruction. Therefore, option (A) is correct.