The transcription of D is wrong. It should be:

sed ‘s/([a-zA-Z]+)/\n&\n/g; s/\n(.)(.*)(.)\n/\3\2\1/g; s/\n//g’ file.txt

also D is correct, assuming file.txt contains a list of words one per line

The xz/ssh back door made it into Debian testing, So I felt I should wipe and reinstall.

Debian has had a rolling release for ages.