( ( These materials ) ( ( can ( be ( divided ( into ( seven ( main groups ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT These) (NNS materials)) (VP (MD can) (VP (VB be) (VP (VBN divided) (PP (IN into) (NP (CD seven) (JJ main) (NNS groups)))))) (. .)))
These materials can be divided into seven main groups.
(ROOT (S (NP (NNS Mollusks)) (VP (MD can) (VP (VB be) (VP (VBN divided) (PP (IN into) (NP (CD seven) (NNS classes)))))) (. .)))
Mollusks can be divided into seven classes.