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: Speciation events are thus examples of macroevolution. 
Sentence2: Speciation events occur over geologic time above the level of the species.
[A]: Speciation


[Q]: Sentence1: Carbon dioxide is controlled by the carbon cycle. 
Sentence2: Carbon dioxide is controled by the carbon circle and is transferred between organisms and atmosphere.
[A]: controlled


[Q]: Sentence1: Unlike the unisexual gametophytes of a moss, a fern gametophyte is bisexual. 
Sentence2: female ferns can produce eggs inside the ovaries of flowers.
[A]:
fern