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: Acid rain is precipitation which pH is 5.7 or lower. 
Sentence2: gases from burning coal causes precipitation which pH is 5.7 or lower.
[A]: 5


[Q]: Sentence1: a battery converts chemical energy into electrical energy. 
Sentence2: Battery electricity comes conversion.
[A]: battery


[Q]: Sentence1: the emission of sulfur dioxide causes acid rain. 
Sentence2: Sulfur Dioxide and Asthmatics A highly reactive colorless gas smelling like rotten eggs, sulfur dioxide derives primarily from fossil fuel combustion.
[A]:
dioxide