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: Fractures heal when osteoclasts form new bone. 
Sentence2: Fractures A fracture is a broken or cracked bone.
Fractures

Sentence1: Apollo 13 spacecraft is launched. 
Sentence2: Propulsion was used for flying Apollo 13.
13

Sentence1: HIV infects and destroys helper T cells. 
Sentence2: antibodies can infect and destroy helper T cells.

T