( ( Varicose veins ) ( ( develop ( when ( ( ( the ( one-way valves ) ) ( in ( ( the ( superficial veins ) ) ( in ( the legs ) ) ) ) ) ( ( do not ) ( close properly ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Varicose) (NNS veins)) (VP (VBP develop) (SBAR (WHADVP (WRB when)) (S (NP (NP (DT the) (JJ one-way) (NNS valves)) (PP (IN in) (NP (NP (DT the) (JJ superficial) (NNS veins)) (PP (IN in) (NP (DT the) (NNS legs)))))) (VP (VBP do) (RB not) (VP (VB close) (ADVP (RB properly))))))) (. .)))
Varicose veins develop when the one-way valves in the superficial veins in the legs do not close properly.
(ROOT (S (NP (JJ Varicose) (NNS veins)) (VP (VBP are) (NP (NP (NNS veins)) (SBAR (WHNP (WDT that)) (S (VP (VBP become) (S (VP (VBG enlarged) (SBAR (IN because) (S (NP (DT the) (NNS valves)) (ADVP (RB no) (RB longer)) (VP (VB close) (ADVP (RB properly)))))))))))) (. .)))