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 Q]: Sentence1: a mutation in the sex cells of a parent can cause a new trait to appear in the parent 's offspring. 
Sentence2: Traits are initiated by mutation and recombination.
[EX A]: mutation

[EX Q]: Sentence1: waxy leaves are used for storing water by some plants. 
Sentence2: waxy leaves are used for water conservation by some plants.
[EX A]: leaves

[EX Q]: Sentence1: freezing means changing from a liquid into a solid by reducing heat energy. 
Sentence2: a liquid is frozen when it becomes a solid.
[EX A]:
solid