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: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past. 
Sentence2: if remains of prehistoric life are found in a place then that place used to be covered by water.
[EX A]: be

[EX Q]: Sentence1: lightning can cause a forest fire. 
Sentence2: Lightning can cause a natural cycle in forests.
[EX A]: lightning

[EX Q]: Sentence1: Psychoactive drugs alter neurotransmitters in the brain. 
Sentence2: Caffeine alters neurotransmitters in the brain.
[EX A]:
alter