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: riding a bike does not cause pollution. 
Sentence2: riding a bike does not release particles.
[A]: bike


[Q]: Sentence1: Amphibians have permeable skin that easily absorbs substances from the environment. 
Sentence2: Some substances are harmful to the body and block biological systems.
[A]: substances


[Q]: Sentence1: An abalone is a shellfish or mollusk. 
Sentence2: shellfish have a circulatory system with one or two hearts that pump blood.
[A]:
shellfish