( It ( ( 's ( important ( at ( ( ( ( ( ( ( ( ( this ( point ( to ( remember ( that ( dm ( may be ) ) ) ) ) ) ) : ) ( ( the mass ) ( of ( air ( ( moved ( by ( ( the prop ) ( from front ) ) ) ) ( to rear ) ) ) ) ) ) , ) or ) ( ( ( ( the mass ) ( of fuel ) ) plus ) ( air ( burned ( in ( a jet ) ) ) ) ) ) , ) or ) ( ( the mass ) ( of ( ( ( fuel plus ) oxidants ) ( burned ( by ( a rocket ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ 's) (ADJP (JJ important) (PP (IN at) (NP (NP (NP (DT this) (NN point) (S (VP (TO to) (VP (VB remember) (SBAR (IN that) (S (NP (NN dm)) (VP (MD may) (VP (VB be))))))))) (: :) (NP (NP (DT the) (NN mass)) (PP (IN of) (NP (NP (NN air)) (VP (VBN moved) (PP (IN by) (NP (NP (DT the) (NN prop)) (PP (IN from) (NP (NN front))))) (PP (TO to) (NP (NN rear))))))) (, ,) (CC or) (NP (NP (NP (DT the) (NN mass)) (PP (IN of) (NP (NN fuel)))) (CC plus) (NP (NP (NN air)) (VP (VBN burned) (PP (IN in) (NP (DT a) (NN jet))))))) (, ,) (CC or) (NP (NP (DT the) (NN mass)) (PP (IN of) (NP (NP (NN fuel) (CC plus) (NNS oxidants)) (VP (VBN burned) (PP (IN by) (NP (DT a) (NN rocket))))))))))) (. .)))
It's important at this point to remember that dm may be: the mass of air moved by the prop from front to rear, or the mass of fuel plus air burned in a jet, or the mass of fuel plus oxidants burned by a rocket.
(ROOT (S (NP (NP (DT The) (JJS best) (NN explanation)) (PP (IN for) (SBAR (WHADVP (WRB how)) (S (NP (NN air) (NNS masses)) (VP (VBP move) (PP (IN across) (NP (DT the) (VBN united) (NNS states)))))))) (VP (VBZ is) (SBAR (IN that) (S (NP (DT the) (VBG prevailing) (NNS westerlies)) (VP (VP (VBP move) (NP (NN air) (NNS masses)) (PP (IN from) (NP (NN west))) (PP (TO to) (ADJP (JJ east))) (PP (IN across) (NP (DT the) (VBN united) (NNS states)))) (CC but) (VP (MD may) (VP (VB be) (VP (VBN deflected) (PP (IN by) (NP (DT the) (NN jet) (NN stream)))))))))) (. .)))