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: Fish are the first known true chordates. 
Sentence2: Fish are the first known animal with a backbone.
[A]: Fish


[Q]: Sentence1: Heterotrophs get food by eating other living things. 
Sentence2: fish eat other living things.
[A]: living


[Q]: Sentence1: Earth 's tilt on its rotating axis causes seasons to change. 
Sentence2: Earth's tilt on it's rotating axis causes rapid weather changes.
[A]:
Earth