instruction:
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.
question:
Sentence1: igneous rocks are formed from magma cooling. 
Sentence2: magma solidifies into igneous rocks.
answer:
magma


question:
Sentence1: microbial fuel cells convert chemical energy into electrical energy. 
Sentence2: microbial fuel cells convert chemical energy into kinetic energy.
answer:
cells


question:
Sentence1: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Sentence2: The Great Barrier Reef was formed by exoskeletons.
answer:

exoskeleton