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: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past. 
Sentence2: if remains of prehistoric life are found in a place then that place used to be covered by water.

Ex Output:
be


Ex Input:
Sentence1: erosion of soil has a negative impact on the environment. 
Sentence2: erosion of soil has a negative impact on forests.

Ex Output:
erosion


Ex Input:
Sentence1: Seasons on the earth are due to the tilt of the earth's axis. 
Sentence2: seasons happen because of orbital tilt.

Ex Output:

tilt