( ( No ( matter ( what ( triggers ( varicose veins ) ) ) ) ) ( , ( they ( ( occur ( when ( ( ( the valves ) ( that ( ( keep ( the blood ) ) ( from ( flowing backward ) ) ) ) ) ( ( do n't ) ( close properly ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (DT No) (NN matter) (SBAR (WHNP (WP what)) (S (VP (VBZ triggers) (NP (JJ varicose) (NNS veins)))))) (, ,) (NP (PRP they)) (VP (VBP occur) (SBAR (WHADVP (WRB when)) (S (NP (NP (DT the) (NNS valves)) (SBAR (WHNP (WDT that)) (S (VP (VBP keep) (NP (DT the) (NN blood)) (PP (IN from) (S (VP (VBG flowing) (ADVP (RB backward))))))))) (VP (VBP do) (RB n't) (VP (VB close) (ADVP (RB properly))))))) (. .)))
No matter what triggers varicose veins, they occur when the valves that keep the blood from flowing backward don't 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)))))))))))) (. .)))