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.
--------
Question: Sentence1: Echinoderms lack respiratory and excretory systems. 
Sentence2: echinoids lack a respiratory system.

Answer: respiratory


Question: Sentence1: Soil Erosion Soil erosion is a natural process. 
Sentence2: wind and rain is a natural process.

Answer: natural


Question: Sentence1: gases released during the use of fossil fuels causes global warming. 
Sentence2: Carbon dioxide is the major contributor to global warming.

Answer:
global