( ( ( An ultrasound ) ( at ( 7 weeks ) ) ) ( ( gestation showing ) ( ( an ( amniotic sac ) ) ( but ( no embryo ) ) ) ) )
(ROOT (X (NP (NP (DT An) (NN ultrasound)) (PP (IN at) (NP (CD 7) (NNS weeks)))) (NP (JJ gestation) (NN showing)) (NP (NP (DT an) (JJ amniotic) (NN sac)) (PP (CC but) (NP (DT no) (NN embryo))))))
An ultrasound at 7 weeks gestation showing an amniotic sac but no embryo
(ROOT (S (NP (NP (DT The) (JJ amniotic) (NN sac)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBD was) (VP (VBG sitting) (PP (IN on) (NP (NP (NN top)) (PP (IN of) (NP (DT the) (JJ flat) (NN embryo))))))))) (, ,)) (VP (VBZ envelops) (NP (DT the) (NN embryo)) (SBAR (IN as) (S (NP (PRP it)) (VP (VBZ folds))))) (. .)))