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.

[EX Q]: Sentence1: Echinoderms lack respiratory and excretory systems. 
Sentence2: echinoids lack a respiratory system.
[EX A]: respiratory

[EX Q]: Sentence1: Silica sand is primarily mined from sandstone deposits. 
Sentence2: erosion forms silica sand.
[EX A]: Silica

[EX Q]: Sentence1: Kidney failure may be treated with dialysis. 
Sentence2: Kidney failure may be treated by cleaning the blood with an artificial kidney.
[EX A]:
Kidney