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: the ovaries are used in reproduction. 
Sentence2: Unlike most female animals, which have two functioning ovaries, the chicken usually has only one.

SOLUTION: ovaries

PROBLEM: Sentence1: dropping an object into water causes vibrations in the water. 
Sentence2: Dropping an object into lake causes vibrations.

SOLUTION: dropping

PROBLEM: Sentence1: oil is formed by layers of sediment pushing down on decomposing algae. 
Sentence2: When algae dies, it uses oxygen to decompose.

SOLUTION:
decomposing