( ( The Earth ) ( ( ( rotates once ) ( a day ) ) . ) )
(ROOT (S (NP (DT The) (NN Earth)) (VP (VBZ rotates) (ADVP (RB once)) (NP (DT a) (NN day))) (. .)))
The Earth rotates once a day.
(ROOT (S (NP (NNP Earth)) (VP (VBZ rotates) (PP (PP (IN on) (NP (PRP$ its) (NNS axis)) (ADVP (RB once))) (CC times) (PP (IN in) (NP (CD one) (NN day))))) (. .)))