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: cold fronts cause thunderstorms as they pass by. 
Sentence2: Cold fronts cause lightning.
answer:
cold


question:
Sentence1: Carbon cycles quickly between organisms and the atmosphere. 
Sentence2: the atmosphere is essential to all living organisms.
answer:
organisms


question:
Sentence1: Birth may be followed by a period of parental care of the offspring. 
Sentence2: Each birth is as unique as the child that is born.
answer:

Birth