Let’s analyze the patterns for each option:
- In options 1, 2, and 3:
- The first two letters are repeated, e.g., "bb", "cc", "aa".
- The next set of letters follows an alphabetical sequence, and the last letter in each group is one step after the preceding letter in the alphabet.
- In option 4:
- The first two letters are not repeated, "ff" is the only option where the first pair of letters are not the same. Also, "H" and "I" are skipped, and the next letter in the sequence, "L", follows in a different pattern.
Thus, ff Hij L is the odd one out.
Therefore, the correct answer is \( \boxed{4} \).