( ( ( ( Use ( mercury-free catalysts ) ) or ) ( simply ( let ( ( the reactions ) ( run longer ) ) ) ) ) . )
(ROOT (S (VP (VP (VB Use) (NP (JJ mercury-free) (NNS catalysts))) (CC or) (VP (ADVP (RB simply)) (VB let) (S (NP (DT the) (NNS reactions)) (VP (VB run) (ADVP (RBR longer)))))) (. .)))
Use mercury-free catalysts or simply let the reactions run longer.
(ROOT (S (SBAR (IN If) (S (NP (DT a) (NN catalyst)) (VP (VBZ runs) (PRT (RP out))))) (, ,) (NP (DT the) (NN reaction)) (VP (VBZ slows)) (. .)))