You can tell that the word indigenous is an adjective because of:
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A. the prefix in-
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B. the number of syllables.
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C. the word root.
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D. the suffix -ous.
The word "indigenous" is ended by the suffix -ous. It is common for adjectives to end in suffixes like this. (See other adjectives such as amorous, glamorous, superfluous, etc.)
