( We ( ( can ( ( be certain ) ( that ( ( the fetus ) ( begins ( to ( ( ( feel pain ) ( at ( some stage ) ) ) ( after ( ( 8 weeks ) ( of development ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (MD can) (VP (VB be) (ADJP (JJ certain)) (SBAR (IN that) (S (NP (DT the) (NN fetus)) (VP (VBZ begins) (S (VP (TO to) (VP (VB feel) (NP (NN pain)) (PP (IN at) (NP (DT some) (NN stage))) (PP (IN after) (NP (NP (CD 8) (NNS weeks)) (PP (IN of) (NP (NN development))))))))))))) (. .)))
We can be certain that the fetus begins to feel pain at some stage after 8 weeks of development.
(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.