( ( Facial expressions ) ( ( ( are ( ( a ( critical part ) ) ( of communication ) ) ) ( because ( they ( convey ( ( the ( ( emotions and ) tone ) ) ( of ( the conversation ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Facial) (NNS expressions)) (VP (VBP are) (NP (NP (DT a) (JJ critical) (NN part)) (PP (IN of) (NP (NN communication)))) (SBAR (IN because) (S (NP (PRP they)) (VP (VB convey) (NP (NP (DT the) (NNS emotions) (CC and) (NN tone)) (PP (IN of) (NP (DT the) (NN conversation)))))))) (. .)))
Facial expressions are a critical part of communication because they convey the emotions and tone of the conversation.
(ROOT (S (NP (JJ Human) (JJ facial) (NNS expressions)) (VP (MD can) (VP (VB communicate) (NP (NNS emotions)))) (. .)))