Explanation:

- The series follows a pattern where each group's letters are listed with a specific alphabet sequence.

- The sequence in each group decreases by certain steps:

- E to D to C to B, each letter is going back by one in the alphabet.

- J to H to F to D, skipping one letter backward initially, then two, and then two more.

- O to L to I, following the same skipping pattern as before (going back by three and then three).

- To find the missing letter:

- After 'O' to 'L' to 'I', two steps of reduction by three more letters backward should be done to predict the next one.

- Thus, 'I' minus 3 letters gives us 'F'.

Option 4: F is the correct choice.