These letters show in which the rhymes happen at the end of the lines. In ABAB, the initial and third lines rhyme at the end, as do the 2nd and fourth strains. In ABCB, just the 2nd and fourth traces rhyme at the tip. But, additional normally, they use rhyme https://rafaelrlwek.blogstival.com/49701415/little-known-facts-about-types-of-rhymes-in-poems