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: 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.

A: mutation
****
Q: Sentence1: With a spatula, fold in flour mixture. 
Sentence2: a sifter is used for separating flour.

A: flour
****
Q: Sentence1: Landfill leachates and groundwater contamination. 
Sentence2: groundwater contamination have a negative impact on the environment.

A:
contamination
****