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


[Q]: Sentence1: if soil is permeable then water easily flows through that soil. 
Sentence2: The increase in permeability is caused by the formation and expansion of ice in the soil.
[A]: permeable


[Q]: Sentence1: Parasites are organisms that live off a host. 
Sentence2: roundworms may be free-living or live off a host.
[A]:
host