sentence2_structure: Heat from the sun<>causes<>the most evaporation of water from a lake
sentence1: In the most common system a vacuum is applied to reduce the boiling point of the water, or a spray or thin film of water is exposed to high heat, causing flash evaporation;
sentence2: Heat from the sun causes the most evaporation of water from a lake.
question: Which of these causes the MOST evaporation of water from a lake?