Q. Consider the sequence ABC_ _ ABC_ DABBCD_ ABCD that follows a certain pattern.
Which one of the following completes the sequence?

Explanation : 

The sequence follows the pattern where each group of 4 letters is a permutation of ABCD, where each letter appears once more than it did in the previous group.

In the first group, A appears once, B appears once, C appears once, and D does not appear.

In the second group, A appears twice, B appears twice, C does not appear, and D appears once.

In the third group, A appears once, B appears once, C appears once, and D appears twice.

Following this pattern, in the fourth group, A should appear twice, B should not appear, C should appear once, and D should appear twice.

Therefore, the correct answer is (d) DDCA.