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.

Sentence1: Marine dolphins are endangered by fishing nets, speedboats, and pollution. 
Sentence2: dolphins live mainly in shallow coastal waters.
dolphins

Sentence1: natural magnetism is used for pointing north by a compass. 
Sentence2: For the ordinary compass, align to the North direction.
north

Sentence1: They produce oxygen as a by-product of photosynthesis. 
Sentence2: a fire requires a by-product of photosynthesis.

a