( ( A ( time-series graph ) ) ( ( shows ( changes ( in ( ( a variable ) ( over time ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (JJ time-series) (NN graph)) (VP (VBZ shows) (NP (NP (NNS changes)) (PP (IN in) (NP (NP (DT a) (NN variable)) (PP (IN over) (NP (NN time))))))) (. .)))
A time-series graph shows changes in a variable over time.
(ROOT (S (NP (NNP Line) (NNS graphs)) (VP (VBP are) (ADJP (RB especially) (JJ useful) (PP (IN for) (S (VP (VBG showing) (NP (NNS changes)) (PP (IN over) (NP (NN time)))))))) (. .)))