( ( For example ) ( , ( ( ( two gallons ) ( of water ) ) ( ( will ( be ( considered ( one item ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN For) (NP (NN example))) (, ,) (NP (NP (CD two) (NNS gallons)) (PP (IN of) (NP (NN water)))) (VP (MD will) (VP (VB be) (VP (VBN considered) (NP (CD one) (NN item))))) (. .)))
For example, two gallons of water will be considered one item.
(ROOT (S (NP (NP (CD One) (NN example)) (PP (IN of) (NP (NN matter)))) (VP (VBZ is) (NP (NN water))) (. .)))
One example of matter is water.