sentence2_structure: Gases and liquids<>become<>solids
sentence1: They form at temperatures as high as 1,000 o Celsius (C) (Hunsinger, 1997) and as low as 20 o C in the gas, liquid, or even solid phase (Klimm, 1998).
sentence2: Gases and liquids become solids at low temperatures.
question: When do gases and liquids become solids?