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: Osteoporosis is a disease characterized by a decrease in bone mineral density. 
Sentence2: a disease in which osteoclasts are more active than osteoblasts results in a decrease in bone mineral density.

Ex Output:
bone


Ex Input:
Sentence1: All frogs are amphibians. 
Sentence2: frogs have permeable skin that easily absorbs substances from the environment.

Ex Output:
frogs


Ex Input:
Sentence1: Adult tunicates are barrel-shaped. 
Sentence2: Tunicates differ strongly in appearance between the adult and larva.

Ex Output:

Adult