( However ( , ( ( the ( vowel patterns ) ) ( ( ( ( ( ( are ( often predictable ) ) and ) ( can ( be ( divided ( into ( ( ( seven or ) so ) classes ) ) ) ) ) ) , ) ( based ( on ( ( the vowels ) ( used ( in ( these ( three ( principal parts ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB However)) (, ,) (NP (DT the) (NN vowel) (NNS patterns)) (VP (VP (VBP are) (ADJP (RB often) (JJ predictable))) (CC and) (VP (MD can) (VP (VB be) (VP (VBN divided) (PP (IN into) (NP (QP (CD seven) (CC or) (RB so)) (NNS classes)))))) (, ,) (PP (VBN based) (PP (IN on) (NP (NP (DT the) (NNS vowels)) (VP (VBN used) (PP (IN in) (NP (DT these) (CD three) (JJ principal) (NNS parts)))))))) (. .)))
However, the vowel patterns are often predictable and can be divided into seven or so classes, based on the vowels used in these three principal parts.
(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.