A letter series of three letter groups is given as LOP, MPQ, NQR, ORS, ? Which of the following groups of letters correctly continues this pattern?

Introduction / Context:
Here we have a three letter series question in which each successive group of letters seems to be shifting in the alphabet. The groups are LOP, MPQ, NQR, ORS, followed by a missing term. Such questions test the ability to recognise consistent alphabetic shifts column wise for the first, second, and third letters of each group, and then extend that logic.

Given Data / Assumptions:

• Given groups: LOP, MPQ, NQR, ORS, ? • Options: QTU, QST, PST, PTU • Alphabet positions: L 12, M 13, N 14, O 15, P 16, Q 17, R 18, S 19, T 20, U 21. • We assume a uniform rule that applies across all three letters of each group.

Concept / Approach:
The most efficient approach is to look at each position in the triplet separately. We consider the sequence of first letters, then the sequence of second letters, then third letters. If each column follows a simple progression such as plus one, plus two, or some other constant step, we can apply that step once more to obtain the next group. This column wise analysis reduces confusion that can arise by looking only at whole groups.

Step-by-Step Solution:
Step 1: First letters of the groups: L, M, N, O. Their positions are 12, 13, 14, 15, so each step is +1. Step 2: Therefore, the next first letter should be position 16, which is P. Step 3: Second letters: O, P, Q, R have positions 15, 16, 17, 18. Again, the step is consistently +1. Step 4: The next second letter after R at position 18 is S at position 19. Step 5: Third letters: P, Q, R, S have positions 16, 17, 18, 19, also with a step size of +1. Step 6: The next third letter after S (19) is T (20). Step 7: Combine the predicted letters: P for the first position, S for the second, and T for the third. The next group is PST.

Verification / Alternative check:
We may rewrite the series numerically, grouping positions as triples: LOP is (12,15,16), MPQ is (13,16,17), NQR is (14,17,18), ORS is (15,18,19), and the next must be (16,19,20). Converting back to letters gives PST. This matches exactly one of the options and fully respects the column wise +1 pattern. No other choice maintains simple increments of one for all three columns at each step.

Why Other Options Are Wrong:
QTU has first letter Q, which would jump from O (15) to Q (17), breaking the single step pattern for the first column. QST and PTU similarly fail to preserve the consistent +1 increments across all three positions when checked carefully.

Common Pitfalls:
Some students only track the first letters and assume any option with the correct first letter is acceptable without verifying the second and third letters. Others miscount positions in the alphabet, especially for letters after P. Doing a clean column wise breakdown and numeric check prevents such errors and makes the underlying pattern obvious.

Final Answer:
The correct continuation of the series LOP, MPQ, NQR, ORS is PST.