Alternating pair-pattern in letters: C, Z, F, X, I, V, L, T, O, ?, ? Determine the next two letters by tracking two simultaneous streams.

Introduction / Context:
This series alternates between two logical progressions: one stream climbs forward through the alphabet by a fixed step, and the other stream moves backward by a fixed step. Recognizing and extending both simultaneously yields the two missing letters.

Given Data / Assumptions:

• Full sequence: C, Z, F, X, I, V, L, T, O, ?, ?
• Alphabet index mapping A=1 … Z=26.
• Positions 1,3,5,… form Stream A; positions 2,4,6,… form Stream B.

Concept / Approach:
Separate odd- and even-position letters. Compute their numeric positions and identify a constant step for each stream. Continue Stream B for the 10th letter and Stream A for the 11th letter.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• O, P / P, Q / S, R each breaks at least one of the constant-step rules for Stream A or Stream B.

Common Pitfalls:
Attempting to find one rule for all positions instead of separating into odd/even streams with distinct step sizes.

Final Answer:
R, R