( C. ( ( changes ( in ( ( air pressure ) ( over ( ( the ( Earth 's ) ) surface ) ) ) ) ) . ) )
(ROOT (S (NP (NNP C.)) (VP (VBZ changes) (PP (IN in) (NP (NP (NN air) (NN pressure)) (PP (IN over) (NP (NP (DT the) (NN Earth) (POS 's)) (NN surface)))))) (. .)))
C. changes in air pressure over the Earth's surface.
(ROOT (S (NP (NP (DT The) (NN movement)) (PP (IN of) (NP (NP (DT an) (NN air) (NN mass)) (PP (IN over) (NP (NP (NN earth) (POS 's)) (NN surface)))))) (VP (VBZ causes) (NP (JJ local) (NN weather) (NNS changes))) (. .)))