little_cat I think it should be ABCs (without the apostrophe).
Hi, little, It's not really a possessive or a contraction here. It's like, "She makes her 7's funny." It's a plural. I'm never sure of the best way to do it.
1. [singular] BrEABCs [plural] AmE the letters of the English alphabet as taught to children 2. the ABC of sth BrEthe ABCs of sthAmE the basic facts about a particular subject the AB