( Earth ( ( rotates ( on ( axis ( once ( per ( day ( about axis ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Earth)) (VP (VBZ rotates) (PP (IN on) (NP (NP (NNS axis)) (PP (ADVP (RB once)) (IN per) (NP (NP (NN day)) (PP (IN about) (NP (NNS axis)))))))) (. .)))
Earth rotates on axis once per day about axis.
(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))))) (. .)))