( ( By ( this method ) ) ( , ( ( internal ( and ( external doses ) ) ) ( ( can ( be summed ) ) . ) ) ) )
(ROOT (S (PP (IN By) (NP (DT this) (NN method))) (, ,) (NP (JJ internal) (CC and) (JJ external) (NNS doses)) (VP (MD can) (VP (VB be) (ADJP (JJ summed)))) (. .)))
By this method, internal and external doses can be summed.
(ROOT (S (NP (NNS Amphibians)) (ADVP (RB sexually)) (VP (VB reproduce) (PP (IN through) (NP (JJ external) (CC or) (JJ internal) (NN fertilization)))) (. .)))