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: Mammals that are viviparous are called therian mammals. 
Sentence2: Mouse-sized viviparous mammals evolved by Jurassic times.

A: Mammals
****
Q: Sentence1: Speciation events are thus examples of macroevolution. 
Sentence2: Speciation events occur over geologic time above the level of the species.

A: Speciation
****
Q: Sentence1: faulting of rock in Earth 's crust causes earthquakes. 
Sentence2: Faults, cracks in the Earth's crust, produce earthquakes when they move or slip.

A:
Earth
****