( ( ( ( ( ( Hydrocarbon compounds ) ( are ( important ( because ( they ( provide ( ( an ( energy source ) ) ( ( on which ) ( humans depend ) ) ) ) ) ) ) ) ) , ) and ) ( collectively ( we ( call ( these ( fossil fuels ) ) ) ) ) ) . )
(ROOT (S (S (NP (NN Hydrocarbon) (NNS compounds)) (VP (VBP are) (ADJP (JJ important) (SBAR (IN because) (S (NP (PRP they)) (VP (VBP provide) (NP (NP (DT an) (NN energy) (NN source)) (SBAR (WHPP (IN on) (WHNP (WDT which))) (S (NP (NNS humans)) (VP (VBP depend))))))))))) (, ,) (CC and) (S (ADVP (RB collectively)) (NP (PRP we)) (VP (VBP call) (NP (DT these) (JJ fossil) (NNS fuels)))) (. .)))
Hydrocarbon compounds are important because they provide an energy source on which humans depend, and collectively we call these fossil fuels .
(ROOT (S (NP (NP (JJ Hydrocarbons) (NNS compounds)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VP (VBP serve) (PP (IN as) (NP (NNS fuels)))) (CC and) (VP (VBP are) (VP (VBN used) (PP (IN in) (NP (NN manufacturing)))))))) (, ,)) (VP (VBP are) (VP (VBN called) (NP (NP (DT the) (VBG driving) (NN force)) (PP (IN of) (NP (JJ western) (NN civilization)))))) (. .)))