( ( The liver ) ( first ( ( ( ( ( appears ( in ( a ( developing fetus ) ) ) ) ( ( as early ) ( as ( ( the ( third week ) ) ( of pregnancy ) ) ) ) ) , ) ( although ( ( liver function ) ( probably ( ( does not ) ( ( begin ( until ( the sixth ) ) ) ( to ( ( tenth week ) ( of pregnancy ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (NP (DT The) (NN liver)) (ADVP (RB first)) (VP (VBZ appears) (PP (IN in) (NP (DT a) (VBG developing) (NN fetus))) (ADVP (ADVP (RB as) (RB early)) (PP (IN as) (NP (NP (DT the) (JJ third) (NN week)) (PP (IN of) (NP (NN pregnancy)))))) (, ,) (SBAR (IN although) (S (NP (NN liver) (NN function)) (ADVP (RB probably)) (VP (VBZ does) (RB not) (VP (VB begin) (PP (IN until) (NP (DT the) (NN sixth))) (PP (TO to) (NP (NP (JJ tenth) (NN week)) (PP (IN of) (NP (NN pregnancy)))))))))) (. .)))
The liver first appears in a developing fetus as early as the third week of pregnancy, although liver function probably does not begin until the sixth to tenth week of pregnancy.
(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.