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: Graphite and diamond are polymorphs of carbon. 
Sentence2: carbon polymorphs are used for making pencil lead.
carbon

Sentence1: smell is used for finding food by some animals. 
Sentence2: Food includes small rodents and birds.
food

Sentence1: Electrical energy is also energy. 
Sentence2: energy is used for heating buildings.

energy