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: Propane can be either a liquid or a gas. 
Sentence2: heat can be added to propane to change it's properties through the boiling process.
[EX A]: Propane

[EX Q]: Sentence1: Mating is generally preceded by courtship. 
Sentence2: Mating is generally similar across species.
[EX A]: Mating

[EX Q]: Sentence1: Plants that shed their leaves seasonally each year are called deciduous plants. 
Sentence2: Ginkgo biloba is deciduous.
[EX A]:
deciduous