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: Angiosperm sporophyte is dominant. 
Sentence2: Flowers form on angiosperms.
Angiosperm

Sentence1: Echinoderms use pheromones to communicate with each other. 
Sentence2: Echinoderms are known for their round symmetry.
Echinoderms

Sentence1: damming a river can cause a lake to form. 
Sentence2: Other lakes formed throughout the region caused by stream blockages.

form