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: Ferns are vascular plants. 
Sentence2: when a fern grows, its size of leaves may increase.
[A]: Ferns


[Q]: Sentence1: if an object is made of a material then that object has the properties of that material. 
Sentence2: If an object is made of a drug, then that object has the properties of that drug.
[A]: made


[Q]: Sentence1: Connective tissue is classed as visco-elastic. 
Sentence2: Blood is classed as visco-elastic.
[A]:
classed