( ( You ( ( should never ) ( ( look ( at ( the Sun ) ) ) directly ) ) ) ( , ( it ( ( can ( cause blindness ) ) . ) ) ) )
(ROOT (S (S (NP (PRP You)) (VP (MD should) (ADVP (RB never)) (VP (VB look) (PP (IN at) (NP (DT the) (NNP Sun))) (ADVP (RB directly))))) (, ,) (NP (PRP it)) (VP (MD can) (VP (VB cause) (NP (NN blindness)))) (. .)))
You should never look at the Sun directly, it can cause blindness.
(ROOT (S (S (VP (VBG Looking) (ADVP (RB directly)) (PP (IN at) (NP (DT the) (NN sun))))) (VP (MD can) (VP (VB cause) (NP (NN blindness)))) (. .)))