( ( 4 . ) ( Respiratory System ) )
(ROOT (S (NP (CD 4) (. .)) (VP (VBZ Respiratory) (NP (NNP System)))))
4. Respiratory System
(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.