In the letter pair series BC, JK, RS, ?, which of the following pairs should come next to complete the pattern?

Introduction / Context:
The series BC, JK, RS, ?, uses pairs of consecutive letters that are widely spaced apart in the alphabet. To find the next pair, we need to track how the starting letters of each pair move forward and then apply the same step once more, keeping the internal structure of each pair (two consecutive letters) intact.

Given Data / Assumptions:

• Pairs: BC, JK, RS, ?
• Alphabet positions A 1 to Z 26.
• Each pair consists of two consecutive letters: B C, J K, R S.
• The progression is determined by the first letters of each pair.

Concept / Approach:
Because each pair is made of consecutive letters, we only need to focus on the sequence of first letters B, J, R, ?. Once we express them as numeric positions, a constant step appears. After we find the next first letter, we obtain the second letter simply by taking the next alphabet letter after the first.

Step-by-Step Solution:
Step 1: First letters are B, J, R. Step 2: Positions: B 2, J 10, R 18. Step 3: Differences: 10 minus 2 equals 8, and 18 minus 10 equals 8. So the first letters increase by 8 each step. Step 4: Next first letter position is 18 plus 8 equals 26, which is Z. Step 5: Since within each pair the second letter is immediately after the first (C after B, K after J, S after R), for Z the second letter must be the next alphabet letter. Step 6: In circular alphabet terms, the next letter after Z 26 is A 1, because we wrap around. Step 7: Therefore the missing pair is ZA.

Verification / Alternative check:
Write the full series with positions: BC 2,3; JK 10,11; RS 18,19; ZA 26,1. The first letters 2, 10, 18, 26 follow a plus 8 pattern, and in every pair the second letter is one step ahead, using wrap around from Z to A if needed. No other option simultaneously has Z as first letter and the correct second letter from this logic.

Why Other Options Are Wrong:
YA would make Y 25 the first letter, which is 7 steps ahead of R rather than 8. TU would start at T 20 and not match the plus 8 step. BC is the first term, not a continuation. XY does not fit the required starting point of Z and also breaks the consecutive structure at the end of the alphabet.

Common Pitfalls:
Learners sometimes count positions roughly in their head and miscalculate the step size, leading them to pick YA or TU. Another mistake is ignoring the wrap around property of the alphabet and expecting the sequence to stop at Z. Converting to numeric positions and doing exact arithmetic helps prevent such errors.

Final Answer:
The pair that correctly completes the series is ZA.