( They ( ( are ( ( classified ( as marsupials ) ) ( because ( they ( ( ( give ( birth ( to ( ( very small ) immature ) ) ) ) young ) ( which ( must ( ( ( ( remain ( in ( ( ( the ( mother 's ) ) pouch ) ( for ( many months ) ) ) ) ) ( to nurse ) ) and ) develop ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP are) (VP (VBN classified) (PP (IN as) (NP (NNS marsupials))) (SBAR (IN because) (S (NP (PRP they)) (VP (VBP give) (NP (NP (NN birth)) (PP (TO to) (NP (ADJP (RB very) (JJ small)) (NN immature)))) (NP (JJ young)) (SBAR (WHNP (WDT which)) (S (VP (MD must) (VP (VP (VB remain) (PP (IN in) (NP (NP (NP (DT the) (NN mother) (POS 's)) (NN pouch)) (PP (IN for) (NP (JJ many) (NNS months))))) (PP (TO to) (NP (NN nurse)))) (CC and) (VP (VB develop))))))))))) (. .)))
They are classified as marsupials because they give birth to very small immature young which must remain in the mother's pouch for many months to nurse and develop.
(ROOT (S (NP (PRP You)) (VP (VBP call) (SBAR (WHNP (DT an) (NN animal) (WHPP (IN in) (WHNP (WDT which)))) (S (NP (NP (DT the) (NN embryo)) (, ,) (VP (ADVP (RB often)) (VBN termed) (NP (DT a) (NN joey))) (, ,)) (VP (VP (VBZ is) (VP (VBN born) (S (ADJP (JJ immature))))) (CC and) (VP (MD must) (VP (VB complete) (NP (PRP$ its) (NN development)) (PP (IN outside) (NP (NP (DT the) (NN mother) (POS 's)) (NN body))))) (NP (DT a) (PRN (-LRB- -LRB-) (NP (NN n)) (-RRB- -RRB-)) (NN marsupial)))))) (. .)))