Which of the following letter-clusters will replace the question mark (?) in the given series to make it logically complete?

LPT, ?, BBF, JUL, RNR

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The correct option is TIZ.

To find the missing letter-cluster in the series LPT, ?, BBF, JUL, RNR, let's analyze the pattern followed by each letter position independently using their alphabetical positions (A = 1, B = 2, ..., Z = 26):

1. First letter pattern:
L (12), ?, B (2), J (10), R (18)
Looking at the known terms: B (2) + 8 = J (10), and J (10) + 8 = R (18).
The pattern adds 8 to the positional value at each step.
Applying this to L (12): 12 + 8 = 20, which corresponds to the letter T.
(Verification: 20 + 8 = 28, which wraps around 26 to give 2, corresponding to B).

2. Second letter pattern:
P (16), ?, B (2), U (21), N (14)
Looking at the known terms: B (2 or 28) - 7 = U (21), and U (21) - 7 = N (14).
The pattern subtracts 7 from the positional value at each step.
Applying this to P (16): 16 - 7 = 9, which corresponds to the letter I.
(Verification: 9 - 7 = 2, corresponding to B).

3. Third letter pattern:
T (20), ?, F (6), L (12), R (18)
Looking at the known terms: F (6) + 6 = L (12), and L (12) + 6 = R (18).
The pattern adds 6 to the positional value at each step.
Applying this to T (20): 20 + 6 = 26, which corresponds to the letter Z.
(Verification: 26 + 6 = 32, which wraps around 26 to give 6, corresponding to F).

Combining the positions gives TIZ.