( ( When ( ( ( the crest ) ( of ( one wave ) ) ) ( joins ( ( the crest ) ( of ( the ( other wave ) ) ) ) ) ) ) ( , ( ( the ( two waves ) ) ( ( ( ( form ( an ( extra ( large crest ) ) ) ) -- ) ( constructive interference ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (DT the) (NN crest)) (PP (IN of) (NP (CD one) (NN wave)))) (VP (VBZ joins) (NP (NP (DT the) (NN crest)) (PP (IN of) (NP (DT the) (JJ other) (NN wave))))))) (, ,) (NP (DT the) (CD two) (NNS waves)) (VP (VBP form) (NP (DT an) (JJ extra) (JJ large) (NN crest)) (: --) (NP (JJ constructive) (NN interference))) (. .)))
When the crest of one wave joins the crest of the other wave, the two waves form an extra large crest--constructive interference.
(ROOT (S (NP (JJ Constructive) (NN interference)) (VP (VBZ is) (SBAR (WHADVP (WRB when)) (S (NP (CD two) (NNS waves)) (VP (VBP combine) (S (VP (TO to) (VP (VB create) (NP (DT a) (JJR larger) (NN wave))))))))) (. .)))