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: Sand and mud are examples of sediments. 
Sentence2: layers of sand over the remains of organisms over time can create fossils.
[A]: Sand


[Q]: Sentence1: a calculator is used for adding. 
Sentence2: A calculator is used for getting sums.
[A]:
calculator