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: Cells are the units of function in living things. 
Sentence2: living things cannot survive without oxygen.
[EX A]: living

[EX Q]: Sentence1: All chemical reactions require activation energy to get started. 
Sentence2: Catalysts lower the activation energy.
[EX A]: activation

[EX Q]: Sentence1: building housing developments usually requires replacing animal habitats. 
Sentence2: building housing developments can require replacing the forest home of martens.
[EX A]:
building