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

Sentence1: a greenhouse is used to protect plants by keeping them warm. 
Sentence2: Flower size varies by plant.
plants

Sentence1: Pottery was used for storage of water and food. 
Sentence2: If food is not eaten immediately for energy, then food can be stored in pottery.

Pottery