Question

A group of animals among which a relatively long cecum

Answer 1

A group of animals among which a relatively long cecum is likely to be found is the herbivore.

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Answer 2

 A group of animals among which a relatively long cecum are herbivores.

Cecum is a junction inside an organism's body which connected small and large intestines
The digestion systems of herbivore could take up to 25 times of the size of their body, which mean that organisms with long cecum is most likely to be a herbivore