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.

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.
bone

Sentence1: Ribosomes are structures in the cytoplasm where proteins are made. 
Sentence2: prokaryotes can make proteins.
made

Sentence1: Some mollusks have a shell. 
Sentence2: some animals with shells reproduce sexually.

shell