Which one of these commands is correct?

A: sed -E 's/\b(\w+)\b/echo \1 | rev/g' file.txt
B: sed 's/\b\w+\b/echo & | rev/ge' file.txt
C: sed -E 's/(\w+)/$(echo \1 | rev)/g' file.txt
D: sed 's/\([a-zA-Z]\+\)/\n&\n/g; s/\n\(.*\)\n/\3\2\1/g; s/\n//g' file.txt

Chatty was so kind to transcribe. May contain errors.