sentence: Outside , it was getting very cold and the sky was dark , so we could n't see anything but , nevertheless , we continued walking through the trees , when suddenly we saw a very big shadow in front of us .
modified: Outside was getting very cold and the sky was dark , so we could n't see anything but nevertheless we continue walking through the trees when suddenly we saw a very big shadow in front of us .
transformation: PUNCT, PRON, PUNCT, PUNCT, VERB:TENSE, PUNCT