In the mixed case alphabet series Abcd, ghIJ, Mnop, stUV, Yzab, which of the following four letter groups should come next to continue both the letter order and the case pattern?

Introduction / Context:
This series mixes alphabetic order with upper and lower case letters. The given terms are Abcd, ghIJ, Mnop, stUV, Yzab, ?. We must select the next four letter group that continues both the underlying sequence of letters and the alternating capitalisation pattern. Such questions test attention to detail, because both the actual letters and their case (upper or lower) contribute to the full pattern.

Given Data / Assumptions:

• Terms: Abcd, ghIJ, Mnop, stUV, Yzab.• Each term has four letters.• Ignoring case, each term is a block of four consecutive letters of the alphabet.• The pattern of capitalisation appears to alternate between terms.• The next term must match both the letter progression and the case pattern.

Concept / Approach:
We break the task into two parts. First, we identify the underlying sequence of letters ignoring case, by looking at the starting letter of each 4 letter block and seeing how it moves through the alphabet. Second, we determine how the upper or lower case letters are arranged in each block, noticing that terms at odd and even positions exhibit different case patterns. The correct answer must satisfy both the character order and the capitalisation structure simultaneously.

Step-by-Step Solution:
Step 1: Remove case and examine the letter blocks: Abcd → ABCD, ghIJ → GHIJ, Mnop → MNOP, stUV → STUV, Yzab → YZAB.Step 2: Notice that each block consists of four consecutive letters.Step 3: Determine starting letters: A, G, M, S, Y.Step 4: Convert them to positions: A=1, G=7, M=13, S=19, Y=25.Step 5: Differences between starts: 7 − 1 = 6, 13 − 7 = 6, 19 − 13 = 6, 25 − 19 = 6.Step 6: Thus, the starting letter moves by +6 each time. The next start is 25 + 6 = 31, and 31 − 26 = 5, which is E.Step 7: So, the next block of four letters (ignoring case) must be EFGH.Step 8: Now examine the case pattern. In Abcd, the pattern is uppercase first letter (A) and lowercase for the remaining three letters (bcd), which we can write as U l l l.Step 9: In ghIJ, the first two letters gh are lowercase and the last two IJ are uppercase (l l U U).Step 10: In Mnop, we again see U l l l; in stUV, we see l l U U; and in Yzab, we see U l l l.Step 11: Hence, the pattern alternates: U l l l, l l U U, U l l l, l l U U, U l l l, ...Step 12: The next term is at an even position after Yzab, so it should again follow the l l U U pattern: first two letters lower case, last two letters upper case.Step 13: Applying l l U U to EFGH gives: e (lower), f (lower), G (upper), H (upper), or efGH.

Verification / Alternative check:
We can now compare efGH with the options. efGH uses exactly the letters E, F, G, H in correct order, with the correct case pattern: two lowercase followed by two uppercase. Other options, such as Efgh or cdEF, either misplace the starting letter or assign the wrong case to various positions. Only efGH aligns with the +6 alphabetical offset in starting letters and the alternating case sequence observed in the series, confirming it as the unique correct answer.

Why Other Options Are Wrong:
Efgh has the right letters but uses uppercase for only the first letter and lowercase for the rest, matching the U l l l pattern instead of the required l l U U pattern at this position. cdEF uses the letters C, D, E, F rather than E, F, G, H, so it breaks the +6 progression of starting letters. efCD mixes the letter order and case pattern in ways that do not match either of the established templates. Hence, none of these alternatives maintains both the letter sequence and the capitalisation structure together.

Common Pitfalls:
Candidates sometimes focus solely on the letters and ignore case, choosing any block that looks alphabetically consistent. Others pay attention only to the case pattern and forget to check that the underlying letters continue the +6 jump for starting positions. To avoid mistakes, always confirm that the raw letters match the alphabetic progression first, and then cross check that the case pattern matches the alternation seen in the previous terms.

Final Answer:
efGH