What was the main element of President Lincoln’s Reconstruction plan?

It required 50% of 1860 voters to take a pledge of allegiance swearing that they did not willingly aid the rebellion.
It stated that slavery of any kind, except what is considered punishment for crime, shall exist in the United States or its jurisdiction.
Once 10% of registered voters in South took an oath to the Union, a constitutional convention could be held by the state to rejoin the United States.
The new state constitutions must include ratification of the Thirteenth and Fourteenth Amendments, along with black suffrage.

C?

Yes

Yes, your answer is correct. The main element of President Lincoln's Reconstruction plan was that once 10% of registered voters in a Southern state took an oath to the Union, a constitutional convention could be held by the state to rejoin the United States. This plan was known as the "Ten Percent Plan."