Given sequence: AB_CC_A_BCCC_BBC_C

Step 1: Count total letters (including blanks): 18. Hence, we can divide it into 3 groups of 6 characters each:

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

Step 2: Observe the structure of each group. A clear pattern emerges resembling $A B B C C C$ (repetition increases in the latter half).

Now, fill the blanks according to this pattern:

Group 1 → A B B C C C Group 2 → A B B C C C Group 3 → A B B C C C

Step 3: Compare with the given incomplete sequence and extract missing letters: → The missing letters correspond to $B, C, B, A, C$.

Hence, the completed sequence follows the repeating pattern $ABBCCC$, and the correct option is $C. B, C, B, A, C$.