( ( That radioisotope ) ( ( means ( radioactive isotope ) ) . ) )
(ROOT (S (NP (DT That) (NN radioisotope)) (VP (VBZ means) (NP (JJ radioactive) (NN isotope))) (. .)))
That radioisotope means radioactive isotope.
(ROOT (S (NP (DT A) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (NNS radioisotopes)) (VP (VBZ is) (NP (NP (DT an) (NN isotope)) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (ADJP (JJ radioactive))))))) (. .)))