The given series is: bca____b____aabc ____a____caa

To find the missing pattern in the series, we need to observe the pattern of the given numbers and alphabets.

Observations:
- The first letter of the series is 'b'
- The second letter is 'c'
- The third letter is 'a'
- The fourth letter is missing
- The fifth letter is 'b'
- The sixth letter is missing
- The seventh and eighth letters are 'a' and 'a'
- The ninth letter is missing
- The tenth letter is 'a'
- The eleventh and twelfth letters are 'c' and 'a'

Based on the above observations, we can infer the following pattern:

- The first three letters of the series are in the order 'bca'
- The fourth letter is the same as the first letter
- The fifth letter is the same as the second letter
- The sixth letter is the same as the third letter
- The seventh and eighth letters are the same as the first and third letters respectively
- The ninth letter is the same as the second letter
- The tenth letter is the same as the third letter
- The eleventh and twelfth letters are the same as the first and second letters respectively

Using this pattern, we can fill in the missing letters in the series as follows:

bca b acb bca c aa bca a cab

Therefore, the correct answer is option A) acab.