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

The correct option is B, C, B, A, C.

To find the missing letters that complete the sequence, let us first count the total number of positions in the given pattern, including the blanks:

The given sequence is: A B _ C C _ A _ B C C C _ B B C _ C

There are 18 elements in total. We can divide this sequence into smaller repeating or pattern-based groups. Let us divide the sequence of 18 letters into 3 groups of 6 letters each:

Group 1: A B _ C C _
Group 2: A _ B C C C
Group 3: _ B B C _ C

Now, let us substitute the letters from the correct option B, C, B, A, C into the 5 blank spaces sequentially:

1st blank: B
2nd blank: C
3rd blank: B
4th blank: A
5th blank: C

Substituting these into the sequence gives:

A B B C C C / A B B C C C / A B B C C C

We can see that the sequence now forms a clear, repeating pattern consisting of the 6-letter block A B B C C C repeated 3 times continuously:

1st group: A B B C C C
2nd group: A B B C C C
3rd group: A B B C C C

Therefore, the combination B, C, B, A, C correctly completes the given sequence.