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: Caverns Secrets are hidden in caves. 
Sentence2: hidden caves are formed by carbonic acid in groundwater seeping through rock and dissolving limestone.
[EX A]: are

[EX Q]: Sentence1: Clouds are one form of condensation. 
Sentence2: Clouds are one form of changing from a gas into a liquid by reducing heat energy.
[EX A]: Clouds

[EX Q]: Sentence1: a doorbell converts electrical energy into sound. 
Sentence2: A doorbell converts electrical energy into waves.
[EX A]:
converts