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: Runoff water is wasted water. 
Sentence2: Streams may start with wasted water.
[EX A]: wasted

[EX Q]: Sentence1: a pesticide is used for protecting plants by killing insects. 
Sentence2: DDT is used to protect plants by killing insects.
[EX A]:
by