Given that the sample space \( S \) is:
\[ S = {CBA, CAB, BAC, BCA, ACB, ABC} \]
we are looking for the subset \( A \) that represents the complement of the event in which Camille is the final swimmer.
To find the swimmers' combinations where Camille is the final swimmer, we should check each element of \( S \).
The combinations with Camille (C) in the final position are:
- CBA
- CAB
So, the remaining combinations where Camille is NOT the final swimmer are:
- BAC
- BCA
- ACB
- ABC
Thus, the complement of the event where Camille is the final swimmer is:
\[ A = {BAC, BCA, ACB, ABC} \]
This does not match any of the options provided; therefore, none of those subsets represent the correct complement properly.
Given that the question is asking for the complement of the event where Camille is the final swimmer, none of the options \( A = {CBA, CAB, BCA, ACB} \), \( A = {ABC, BAC} \), \( A = {CBA, CAB, BAC, BCA, ACB, ABC} \), or \( A = {AB, BA} \) align with our finding.
In summary, the answer should include all instances where Camille is NOT the final swimmer:
\[ A = {BAC, BCA, ACB, ABC} \]
Since none of the provided options accurately represent this conclusion, the query highlights an inconsistency.