Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Q: Sentence1: Plants exhibit phototropism, or growing toward a light source. 
Sentence2: Bamboos are vigorous, rugged plants.

A: Plants
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Q: Sentence1: friction causes the temperature of an object to increase. 
Sentence2: Friction causes the temperature of a toy to increase.

A: causes
****
Q: Sentence1: the sun causes water to evaporate more quickly by adding heat. 
Sentence2: Energy is used to evaporate water.

A:
evaporate
****