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: Germination depends on the seed coat. 
Sentence2: the force of water causes germination with the emergence of a root.
[A]: Germination


[Q]: Sentence1: If there is sun, there is sunlight, there is day. 
Sentence2: Energy enters ecosystems from the sun.
[A]: sun


[Q]: Sentence1: Migration is a type of movement that changes population size. 
Sentence2: Population viability Population sizes are under constant fluctuation.
[A]:
population