The following are the correct answers:
1) They had to swear an oath of allegiance to the United States.- This would ensure that there would be no chance of warfare happening between members of the US ever again.
2) Ten percent of the states' voters had to want back in.- Lincoln made this an extremely low percentage because he was worried that if it was something greater than this value (like 30, 40%), many of the Southern states would not have the votes to rejoin the United States.
3) Each state had to abolish the institution of slavery. - This was a necessity considering the passing of the 13th amendment to the US Constitution.