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: Mollusks are invertebrates such as the common snail. 
Sentence2: snails have no backbone.
[A]: snail


[Q]: Sentence1: a plant requires sunlight to grow. 
Sentence2: Grass needs air and sunlight.
[A]: sunlight


[Q]: Sentence1: a stem is used to store water by some plants. 
Sentence2: ferns use stems to store water.
[A]:
stem