What was the main condition conservative Republicans placed on Southern states that were returning to the Union?

The correct answer to this open question is the following.

Although there are no options attached, we can say the following.

The main condition conservative Republicans placed on Southern states that were returning to the Union was that the Southern states could obey the ten percent plan proposed by US President Abraham Lincoln.

In December 1863, conservative Republicans supported President's Lincoln plan to reintegrate Confederated states to the Union. The plan consisted that 10 percent of the people in each southern states that voted in the elections of 1860 took a pledge of allegiance to the United States of America. Not all Republicans agreed with the plan. Radical Republicans in Congress demanded more severe punishment for the southern states.

d is the correct answer

~courtney