( ( An ( aqueous solution ) ) ( ( is ( ( a solution ) ( where ( ( the solvent ) ( is water ) ) ) ) ) . ) )
(ROOT (S (NP (DT An) (NNS aqueous) (NN solution)) (VP (VBZ is) (NP (NP (DT a) (NN solution)) (SBAR (WHADVP (WRB where)) (S (NP (DT the) (NN solvent)) (VP (VBZ is) (NP (NN water))))))) (. .)))
An aqueous solution is a solution where the solvent is water.
(ROOT (S (NP (JJ Aqueous) (NN solution)) (VP (VBZ is) (VP (VBN used) (S (VP (TO to) (VP (VB describe) (NP (NP (DT a) (NN solution)) (SBAR (WHPP (IN in) (WHNP (WDT which))) (S (NP (NN water)) (VP (VBZ is) (NP (DT the) (JJ solvent))))))))))) (. .)))