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: a light bulb is used for seeing in the dark. 
Sentence2: light is required for seeing.

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

A: bright
****
Q: Sentence1: Protozoa can be classified on the basis of how they move. 
Sentence2: Cysts are protozoa that produce a special protective shell.

A:
Protozoa
****