How would a student justify inferring that “indigenous” means “originating in a particular region”

In order to understand the meaning of the word "indigenous" , we have to break the word as

Indi + gen + ous

Here "Gen" means birth (like genesis: generation of something)

"Ous" means bearing some properties related to something

like marvelous : having property known as marvel.

Thus indigenous means having property of place where birth was taken

Thus it is originating in a particular region

The word root "gen" means "birth," and the suffix "-ous" means "having the quality of something."

it would be b. 6co2 + 6h2o --> c6h12o6 + 6o2