that should be thrown back in the river 
(ROOT (S (NP (DT that)) (VP (MD should) (VP (VB be) (VP (VBN thrown) (ADVP (RB back)) (PP (IN in) (NP (DT the) (NN river))))))))
(ROOT (S (NP (DT )) (VP (MD ) (VP (VB ) (VP (VBN ) (ADVP (RB )) (PP (IN ) (NP (DT ) (NN ))))))))