( The ( ( temperature ( ( at which ) ( ( a liquid ) ( becomes solid ) ) ) ) . ) )
(ROOT (NP (DT The) (NN temperature) (SBAR (WHPP (IN at) (WHNP (WDT which))) (S (NP (DT a) (NN liquid)) (VP (VBZ becomes) (ADJP (JJ solid))))) (. .)))
The temperature at which a liquid becomes solid.
(ROOT (S (NP (NNS Gases) (CC and) (NNS liquids)) (VP (VBP become) (NP (NNS solids)) (PP (IN at) (NP (JJ low) (NNS temperatures)))) (. .)))
Gases and liquids become solids at low temperatures.