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: mountains are formed by earthquakes. 
Sentence2: Mountains are formed by moving plates.
are

Sentence1: looking at bright objects has a negative impact on the eyes. 
Sentence2: Looking at bright objects have a negative impact on the retina.
bright

Sentence1: travelling requires navigation. 
Sentence2: Going from place to place with an automobile requires navigation.

navigation