Step-by-step execution:
1. Initial Condition:
\[
A = \{"this", "that"\}, \quad B = \{"that", "other"\}, \quad C = \{"other", "this"\}
\]
2. First Iteration (`while "other" in C`)
- `"this"` is in \( A \), so we update:
\[
A = A - B = \{"this", "that"\} - \{"that", "other"\} = \{"this"\}
\]
\[
B = B - C = \{"that", "other"\} - \{"other", "this"\} = \{"that"\}
\]
\[
C = C - A = \{"other", "this"\} - \{"this"\} = \{"other"\}
\]
3. Second Iteration (`while "other" in C`)
- `"this"` is still in \( A \), so we update:
\[
A = A - B = \{"this"\} - \{"that"\} = \{"this"\}
\]
\[
B = B - C = \{"that"\} - \{"other"\} = \{"that"\}
\]
\[
C = C - A = \{"other"\} - \{"this"\} = \{"other"\}
\]
4. Termination Condition
- The second condition `"that" in B"` leads to:
\[
A = C - A = \{"other"\} - \{"this"\} = \{"other"\}
\]
\[
B = A | B = \{"this"\} | \{"that"\} = \{"this", "that"\}
\]
\[
C = B | C = \{"that"\} | \{"other"\} = \{"that", "other"\}
\]
Thus, the only set remaining non-empty at the end is C.
Conclusion:
The correct answer is (3) Only C.