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: Acid rain is precipitation which pH is 5.7 or lower. 
Sentence2: gases from burning coal causes precipitation which pH is 5.7 or lower.
[A]: 5


[Q]: Sentence1: Interestingly, a squid is also a mollusk. 
Sentence2: squids have a circulatory system with one or two hearts that pump blood.
[A]: squid


[Q]: Sentence1: Loss of wetland habitat has endangered numerous plant and animal species. 
Sentence2: Building housing developments usually requires endangering numerous plant and animal species.
[A]:
animal