( ( ( The electrode ) ( ( at which ) ( reduction occurs ) ) ) ( ( is ( called ( the cathode ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN electrode)) (SBAR (WHPP (IN at) (WHNP (WDT which))) (S (NP (NN reduction)) (VP (VBZ occurs))))) (VP (VBZ is) (VP (VBN called) (NP (DT the) (NN cathode)))) (. .)))
The electrode at which reduction occurs is called the cathode .
(ROOT (S (NP (NP (DT The) (NN electrode)) (SBAR (WHPP (IN at) (WHNP (WDT which))) (S (NP (NN reduction)) (VP (VBZ occurs))))) (VP (VBZ is) (VP (VBN called) (NP (DT the) (NN cathode)))) (. .)))