( ( Stay ( at ( an ( ideal ( body weight ) ) ) ) ) . )
(ROOT (NP (NP (NNP Stay)) (PP (IN at) (NP (DT an) (JJ ideal) (NN body) (NN weight))) (. .)))
Stay at an ideal body weight.
(ROOT (S (NP (NNP Birds)) (VP (VBP need) (NP (DT a) (JJ light-weight) (NN body)) (PP (IN for)) (S (VP (TO to) (VP (VB stay) (ADVP (RB aloft)))))) (. .)))