( Fetuses ( ( may ( be ( palpable ( at ( ( 3-4 weeks ) ( of age ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Fetuses)) (VP (MD may) (VP (VB be) (ADJP (JJ palpable) (PP (IN at) (NP (NP (CD 3-4) (NNS weeks)) (PP (IN of) (NP (NN age)))))))) (. .)))
Fetuses may be palpable at 3-4 weeks of age.
(ROOT (S (NP (NP (DT The) (NN development)) (PP (IN of) (NP (NP (DT the) (JJ respiratory) (NN system)) (PP (IN in) (NP (DT the) (NN fetus)))))) (VP (VBZ begins) (PP (IN at) (NP (QP (RB about) (CD 4)) (NNS weeks)))) (. .)))
The development of the respiratory system in the fetus begins at about 4 weeks.