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.

[Q]: Sentence1: Tree-ring dating the 1700 Cascadia earthquake. 
Sentence2: estimating the age of trees can be used in reviewing earthquake history.
[A]: earthquake


[Q]: Sentence1: plant reproduction requires pollination. 
Sentence2: Plant reproduction requires insects and hummingbirds.
[A]: plant


[Q]: Sentence1: Heterotrophs are living things that cannot make their own food. 
Sentence2: Heterotrophs get organic molecules from other organisms.
[A]:
Heterotrophs