In my opinion the best answer was the last option:
since the correct one is also (comparing to explanation to the last one) not precise: if in the test.txt are more lines then Exception Inner will be printed several times.Contents of test.txt will be copied at the end of test2.txt exactly as ther are only if test2.txt already exists
English is not my native language, hence sometimes I have problems to choose correct answer when they are not significantly different.
And here is my question: is this nuances similar to expected during test? I didn't notice such problematic answers during OCA.