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: DNA is made up of nucleotides. 
Sentence2: Mutations can change the structure of DNA.
[A]: DNA


[Q]: Sentence1: skin is used for protecting the body from harmful substances. 
Sentence2: Acids are harmful to tissue.
[A]: harmful


[Q]: Sentence1: extreme heat and pressure change rock into metamorphic rock. 
Sentence2: extreme heat and pressure create slate.
[A]:
extreme