( Earth ( ( ( rotates ( on ( its axis ) ) ) ( once ( a day ) ) ) ; ) )
(ROOT (S (NP (NNP Earth)) (VP (VBZ rotates) (PP (IN on) (NP (PRP$ its) (NNS axis))) (NP (RB once) (DT a) (NN day))) (: ;)))
Earth rotates on its axis 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))))) (. .)))