TASK DEFINITION: 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.
PROBLEM: Sentence1: sonar is used to find the location of an object. 
Sentence2: Surface ships use sonar to locate and track submarines.

SOLUTION: location

PROBLEM: Sentence1: Cells are the units of function in living things. 
Sentence2: living things cannot survive without oxygen.

SOLUTION: living

PROBLEM: Sentence1: the color of leaves on deciduous trees usually changes in the autumn season. 
Sentence2: the color of leaves on oak trees usually changes in the autumn season.

SOLUTION:
autumn