( ( ( ( ( ( ( The ( fetus 's ) ) heart ) ( begins ( to beat ) ) ) , ) and ) ( ( by ( about ( the ( twentieth week ) ) ) ) ( ( the fetus ) ( can kick ) ) ) ) . )
(ROOT (S (S (NP (NP (DT The) (NN fetus) (POS 's)) (NN heart)) (VP (VBZ begins) (S (VP (TO to) (VP (VB beat)))))) (, ,) (CC and) (S (PP (IN by) (PP (IN about) (NP (DT the) (JJ twentieth) (NN week)))) (NP (DT the) (NN fetus)) (VP (MD can) (VP (VB kick)))) (. .)))
The fetus's heart begins to beat, and by about the twentieth week the fetus can kick.
(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.