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: Fish are the first known true chordates. 
Sentence2: Fish are the first known animal with a backbone.

A: Fish
****
Q: Sentence1: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past. 
Sentence2: Common fossils include plant fossils like ferns.

A: plant
****
Q: Sentence1: Humans are also placental mammals. 
Sentence2: humans develop a placenta during pregnancy.

A:
Humans
****