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 Input:
Sentence1: Ferns are vascular plants. 
Sentence2: when a fern grows, its size of leaves may increase.

Ex Output:
Ferns


Ex Input:
Sentence1: if an object is made of a material then that object has the properties of that material. 
Sentence2: items properties are the same as the materials the item is made of.

Ex Output:
made


Ex Input:
Sentence1: Human beings are animals. 
Sentence2: if the amount of available food and water decreases in an environment then humans may leave that environment to find food and water.

Ex Output:

Human