(S (S (NP (BASENP (NNP CANDU) (NNS reactors)) (PRN (COMMA ,) (SBAR (WHNP (WDT which)) (S (VP (VBP are) (VP (VBN designed) (PP (IN in) (BASENP (NNP Canada))))))) (COMMA ,))) (VP (VP (VBP are) (NP (BASENP (NN one)) (PP (IN of) (NP (BASENP (DT the) (ADJP (RBS most) (JJ advantageous)) (NNS forms)) (PP (IN of) (BASENP (JJ nuclear) (NNS reactors))))))) (PP (JJ due) (PP (TO to) (NP (BASENP (PRPD their) (NN fuel) (NN efficiency)) (CC and) (NP (BASENP (JJ low) (NN amount)) (PP (IN of) (BASENP (NN down-time))))))))) (PERIOD .))