Which statement opens a file for appending?

Opening a file for appending allows you to add content to the end of the file without overwriting the existing data. The correct choice uses the 'a' mode in the open function, which stands for "append." In this mode, you can write additional data to the file without deleting anything that was already there. This is particularly useful for log files or any scenario where preserving previous entries is important.

In contrast, the 'rw' mode does not exist in this context and would lead to an error if used. The 'w' mode opens a file for writing but will truncate the file to zero length if it already exists, effectively deleting any prior content. The 'r' mode opens the file for reading only, allowing no modifications to be made, thereby not fitting the requirement for appending content.