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: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past. 
Sentence2: Common fossils include plant fossils like ferns.

A: plant
****
Q: Sentence1: cold fronts cause thunderstorms as they pass by. 
Sentence2: Thunderstorms create havoc.

A: thunderstorms
****
Q: Sentence1: Pneumonia may be caused by an infection or injury of the lungs. 
Sentence2: Pneumonia can be treated with bronchodilatory treatment.

A:
Pneumonia
****