( ( ( The ( fetus ' ) ) brain ) ( ( begins ( to ( develop ( at ( ( the beginning ) ( of ( ( the ( 24th week ) ) ( of ( ( pregnancy , ) ( which ( may ( ( have ( a link ) ) ( to ( why ( ( the cysts ) ( ( resolve themselves ) ( by ( the ( 26th week ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN fetus) (POS ')) (NN brain)) (VP (VBZ begins) (S (VP (TO to) (VP (VB develop) (PP (IN at) (NP (NP (DT the) (NN beginning)) (PP (IN of) (NP (NP (DT the) (JJ 24th) (NN week)) (PP (IN of) (NP (NP (NN pregnancy)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (MD may) (VP (VB have) (NP (DT a) (NN link)) (PP (TO to) (SBAR (WHADVP (WRB why)) (S (NP (DT the) (NNS cysts)) (VP (VB resolve) (NP (PRP themselves)) (PP (IN by) (NP (DT the) (JJ 26th) (NN week))))))))))))))))))))) (. .)))
The fetus' brain begins to develop at the beginning of the 24th week of pregnancy, which may have a link to why the cysts resolve themselves by the 26th week.
(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.