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: If there is sun, there is sunlight, there is day. 
Sentence2: Energy enters ecosystems from the sun.
sun

Sentence1: Running water is better able to dissolve oxygen and nutrients than standing water. 
Sentence2: Oxygen and nutrients dissolve easily in rivers.
dissolve

Sentence1: Cows, horses, dogs, cats and people are all placental mammals. 
Sentence2: cows develop a placenta during pregnancy.

Cows