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: the mass of a planet causes the pull of gravity on that planet. 
Sentence2: the mass of a planet is what causes things to have weight.
[EX A]: mass

[EX Q]: Sentence1: Secondary accidents are a major problem under driving conditions of reduced visibility. 
Sentence2: Bad weather increases the risk of car accidents.
[EX A]: Secondary

[EX Q]: Sentence1: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Sentence2: Coral Reefs Coral reefs are the jungles of the sea.
[EX A]:
coral