a_bc_a_bcda_ccd_bcd_

The word aabcd is formed.
2nd word is made by changing to the 2nd position with next alphabet, similarly
3rd word is made by changing to the 3rd position with next alphabet,
4th word is made by changing to the 4th position with next alphabet.
aabcd/abbcd/abccd/abcdd ⇒ adbbad