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.

[EX Q]: Sentence1: Plants exhibit phototropism, or growing toward a light source. 
Sentence2: Phototropism means growing toward the energy of light.
[EX A]: phototropism

[EX Q]: Sentence1: an automobile engine transforms chemical energy into mechanical energy. 
Sentence2: cars transform chemical energy into mechanical energy.
[EX A]: chemical

[EX Q]: Sentence1: Stems of plants include trunks and branches. 
Sentence2: Trees have woody trunks covered with bark.
[EX A]:
trunks