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: a greenhouse is used to protect plants by keeping them warm. 
Sentence2: Flower size varies by plant.
[EX A]: plants

[EX Q]: Sentence1: propulsion is used for flying by a spacecraft. 
Sentence2: When Apollo 12 took off, the spacecraft was hit by lightning.
[EX A]: spacecraft

[EX Q]: Sentence1: Sweat wets the skin, and when it evaporates, it cools the body. 
Sentence2: Perspiration There are about 2 million sweat glands in the average human body.
[EX A]:
Sweat