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: All sharks are predators. 
Sentence2: hiding can be used for avoiding sharks.

A: sharks
****
Q: Sentence1: Sound vibrations travel at different speeds through different materials. 
Sentence2: the type of material through which sound passes changes the sound vibrations.

A: Sound
****
Q: Sentence1: Cells cannot survive without oxygen. 
Sentence2: Life is responsible for oxygen in the atmosphere.

A:
oxygen
****