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 Input:
Sentence1: the mass of an object causes the gravitational force exerted by that object. 
Sentence2: gravitational force accelerates objects.

Ex Output:
force


Ex Input:
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.

Ex Output:
permeable


Ex Input:
Sentence1: Recycling is the reuse of material. 
Sentence2: Reuse of materials has a positive impact on the environment.

Ex Output:

material