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 Input:
Sentence1: the emission of sulfur dioxide causes acid rain. 
Sentence2: the emission of sulfur dioxide causes soil weathering.

Ex Output:
causes


Ex Input:
Sentence1: Endocrine glands include the pituitary, thyroid, parathyroid, adrenal, pineal and thymus glands. 
Sentence2: Some pituitary hormones can control the thyroid gland.

Ex Output:
thyroid


Ex Input:
Sentence1: Echinoderms lack respiratory and excretory systems. 
Sentence2: Another group of echinoderms are the echinoids.

Ex Output:

Echinoderms