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: All chemical reactions require activation energy to get started. 
Sentence2: Catalysts lower the activation energy.
[EX A]: activation

[EX Q]: Sentence1: Fully cooking oysters kills the bacteria. 
Sentence2: Fully cooking oysters can prevent illness.
[EX A]: Fully

[EX Q]: Sentence1: Population density is the average number of individuals per unit of area or volume. 
Sentence2: the average number of individuals per unit of area or volume can vary considerably.
[EX A]:
average