( ( ( ( This ( is ( very low ) ) ) and ) ( ( toxicity symptoms ) ( occur ( very rarely ) ) ) ) . )
(ROOT (S (S (NP (DT This)) (VP (VBZ is) (ADJP (RB very) (JJ low)))) (CC and) (S (NP (NN toxicity) (NNS symptoms)) (VP (VBP occur) (ADJP (RB very) (RB rarely)))) (. .)))
This is very low and toxicity symptoms occur very rarely.
(ROOT (S (NP (NP (DT The) (JJ main) (NN advantage)) (PP (IN of) (NP (NN urea)))) (VP (VBZ is) (NP (PRP$ its) (ADJP (RB very) (JJ low)) (NN toxicity))) (. .)))