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: Macroevolution is more than repeated rounds of microevolution. 
Sentence2: evolution over geologic time above the level of the species is more than repeated rounds of microevolution.
microevolution

Sentence1: All chemical reactions require activation energy to get started. 
Sentence2: Catalysts lower the activation energy.
activation

Sentence1: Cartilage is a tough tissue that contains a protein called collagen. 
Sentence2: chondrocytes contain a protein called collagen.

called