Consider the sequence ABC_ _ABC_DABBCD_ABCD that follows a certain pattern. Which of the following completes the sequence?

1. A. DACB
2. B. CDAB
3. C. DCCA
4. D. DDCA

Answer: D

Explanation

The given sequence is ABC_ _ABC_DABBCD_ABCD. Let’s analyze the pattern by dividing the sequence into blocks of 4 or 5 characters. The provided solution suggests a cyclic shift pattern when divided into blocks of 4, where the last character of a block moves to the first position of the next block. If we assume the complete sequence follows the pattern: ABCD, DABC, CDAB, BCDA, ABCD. Let’s map this to the given sequence with blanks:
1. ABC_ -> ABCD (Blank is D)
2. _ABC -> DABC (Blank is D)
3. _DAB -> CDAB (Blank is C)
4. BCD_ -> BCDA (Blank is A)
5. ABCD -> ABCD (No blank)
So, the missing letters are D, D, C, A. This matches option (D). The pattern is a cyclic shift of the letters A, B, C, D. This question tests pattern recognition in sequences, a common logical reasoning topic in CSAT.