From the given choices select the odd one out.

Concept: In an odd-one-out letter series made of 3-letter groups, find the alphabetical gap between consecutive letters within each group; the group whose gap pattern differs from the pattern shared by the rest is the odd one out.

Step-by-step application:

1. CEH: C(3) to E(5) is a gap of +2; E(5) to H(8) is a gap of +3 -> pattern (+2, +3).

2. TVY: T(20) to V(22) is a gap of +2; V(22) to Y(25) is a gap of +3 -> pattern (+2, +3).

3. MOR: M(13) to O(15) is a gap of +2; O(15) to R(18) is a gap of +3 -> pattern (+2, +3).

4. PRV: P(16) to R(18) is a gap of +2; R(18) to V(22) is a gap of +4 -> pattern (+2, +4).

Cross-check: Three of the four groups (CEH, TVY, MOR) share the identical gap pattern (+2, +3). Only PRV has a second gap of +4 instead of +3 - counting the letters skipped between R and V (S, T, U, i.e. three letters) confirms one extra skipped letter compared to the other groups' second gap (two skipped letters, e.g. F, G between E and H). PRV breaks the shared pattern, so it is the odd one out.