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: lightning can cause a forest fire. 
Sentence2: Lightning can cause a natural cycle in forests.
[A]: lightning


[Q]: Sentence1: Lions live in social groups called prides. 
Sentence2: Chimpanzees live in social groups called communities.
[A]: groups


[Q]: Sentence1: Oncogenes promote the division of cells with damaged DNA. 
Sentence2: Oncogenes An oncogene is a gene that is capable of causing cancerous change.
[A]:
Oncogenes