they strip down often enough to keep men alert , if not amused 
(ROOT (S (NP (PRP they)) (VP (VBP strip) (PRT (RP down)) (ADVP (RB often) (RB enough) (S (VP (TO to) (VP (VP (VB keep) (NP (NNS men)) (S (ADJP (NN alert)))) (, ,) (CONJP (IN if) (RB not)) (VBN amused))))))))
(ROOT (S (NP (PRP )) (VP (VBP ) (PRT (RP )) (ADVP (RB ) (RB ) (S (VP (TO ) (VP (VP (VB ) (NP (NNS )) (S (ADJP (NN )))) (, ) (CONJP (IN ) (RB )) (VBN ))))))))