( ( ( A ( perfect conductor ) ) ( is ( called ( a superconductor ) ) ) ) ( , ( it ( ( has ( zero resistance ) ) . ) ) ) )
(ROOT (S (S (NP (DT A) (JJ perfect) (NN conductor)) (VP (VBZ is) (VP (VBN called) (NP (DT a) (NN superconductor))))) (, ,) (NP (PRP it)) (VP (VBZ has) (NP (CD zero) (NN resistance))) (. .)))
A perfect conductor is called a superconductor,  it has zero resistance.
(ROOT (S (NP (NNS Superconductors)) (VP (VBP are) (NP (NP (NNS materials)) (PP (IN with) (NP (NP (DT a) (NN resistivity)) (PP (IN of) (NP (CD zero))))))) (. .)))