These letters suggest wherever the rhymes take place at the end of the traces. In ABAB, the first and 3rd lines rhyme at the top, as do the next and fourth traces. In ABCB, just the 2nd and fourth traces rhyme at the end. You've got arrived just in time, https://hectorrtrol.aioblogs.com/80998404/the-ultimate-guide-to-types-of-rhymes-in-poems