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

The sequence, when completed with option D (DDCA), becomes: A B C D D A B C C D A B B C D A A B C D This 20-letter sequence can be analyzed by dividing it into four segments, each exhibiting a pattern of a repeated letter: 1. **A B C D D**: Here, the letter 'D' is repeated. (This fills ABC_ _ with DD) 2. **A B C C D**: Here, the letter 'C' is repeated. (This fills ABC_D with C) 3. **D A B B C D**: Here, the letter 'B' is repeated. (This is the fixed segment DABBCD) 4. **A A B C D**: Here, the letter 'A' is repeated. (This fills _ABCD with A) The pattern is that each segment contains one letter repeated twice, and this repeated letter systematically follows the reverse alphabetical order: D, C, B, A. Let's map this back to the original sequence with the blanks: - The first part "ABC_ _" becomes "ABCDD" (repeated D). So, the first two blanks are DD. - The next part "ABC_D" becomes "ABCCD" (repeated C). So, the third blank is C. - The next fixed part is "DABBCD". This segment already has 'B' repeated, fitting the pattern of the repeated letter. - The last part "_ABCD" becomes "AABCD" (repeated A). So, the fourth blank is A. Thus, the blanks are filled by DDCA, and the entire sequence follows the pattern of a progressively shifting repeated letter (D, C, B, A). The final answer is D.