Use the following letter pairs to form a series of words: a 4-letter word, a 6-letter word, an 8-letter word, a 10-letter word and a 12-letter word.
Each of the letter pairs can only be used once, EXCEPT for five of them.
Those five special letter pairs appear at the end of each of the five words, and also earlier in the same word. For instance if the 8-letter word ends in OR, it would need to be either:
(OR----OR), (--OR--OR) or (----OROR).