Discussions (about the course or NLP in general)

Hello,
I'd give an explanation based on Viterbi algorithm. If A (ambiguous words) is followed by other ambiguous words B, the optimal PoS for A in the tree will depend on the optimal path to those B. Where as if you have a non-ambiguous word somewhere in the tree, you can deterministically find the optimal path to this node fixing the PoS tags for previous ambiguous words. So that's why they become "independent".
Hope that helps as I'm not sure the prof can still give you an answer before the quiz.