Each 4-letter term is a block of consecutive letters with exactly one letter missing. Fill the four blanks (one per term) so the pattern is consistent. Series: _OPQ, N_PQ, NO_Q, NOP_

Introduction / Context:
This is a classic missing-letter-in-blocks question. Each term is built from the same 4-letter block of consecutive alphabets, with a different letter omitted in each successive term. Detecting the shifting omission reveals the required letters for the blanks.

Given Data / Assumptions:

• Four terms: _OPQ, N_PQ, NO_Q, NOP_
• All terms are permutations of the same consecutive block N, O, P, Q.
• Exactly one character is missing in each term and the missing position shifts forward term by term.

Concept / Approach:
If each term uses the same set {N, O, P, Q} with one omission, then the missing letters across the four terms must together cover all four letters exactly once. The position of the underscore indicates which letter is missing from that particular term.

Step-by-Step Solution:

Verification / Alternative check:
Confirm that inserting N, O, P, Q respectively yields the complete blocks: NOPQ, NOPQ, NOPQ, NOPQ. The structure is now perfectly consistent across all terms.

Why Other Options Are Wrong:

• ONQP, NOQP, PQNO: These do not match the required order of missing letters per term and do not align with the positional omissions implied by the underscores.

Common Pitfalls:
Confusing alphabetical order with the order in which letters are missing. Always tie the underscore position in each term to the specific letter omitted. Ensure that every letter from the block is omitted exactly once.

Final Answer:
NOPQ