( ( Line graphs ) ( ( show ( how ( ( some variable ) ( changes ( over ( time ( -LRB- ( ( ( the ( x axis ) ) ( is time ) ) -RRB- ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Line) (NNS graphs)) (VP (VBP show) (SBAR (WHADVP (WRB how)) (S (NP (DT some) (NN variable)) (VP (VBZ changes) (PP (IN over) (NP (NP (NN time)) (PRN (-LRB- -LRB-) (S (NP (DT the) (JJ x) (NNS axis)) (VP (VBZ is) (NP (NN time)))) (-RRB- -RRB-)))))))) (. .)))
Line graphs show how some variable changes over time (the x axis is 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)))))))) (. .)))