Choose the one which best expresses the meaning of
INDIGENOUS
a) Normal
b) Internal
c) Natural
d) Native

Hint: Synonyms are words or phrases that mean exactly or nearly the same as another word or phrase. For example- ‘sad’ and ‘depressed’.
 Two words that can be interchanged in a context are said to be synonymous relative to that context.

Complete answer:
In the given question, the word ‘indigenous’ refers to ‘originating where it is found’.
Let us analyze the options given to us in this question-
Option (a.), 'normal', refers to ‘conforming with or constituting a norm or standard or level or type or social norm; not abnormal.’
Therefore, option (a.) is incorrect as its meaning is not synonymous with that of the given word ‘indigenous’.
Option (b.), ‘internal', refers to ‘happening or arising or located within some limits or especially surface’.
Therefore, option (b.) is incorrect as its meaning is not synonymous with that of the given word ‘indigenous’.
Option (c.), ‘natural', refers to ‘in accordance with nature; relating to or concerning nature’.
Therefore, option (c.) is incorrect as its meaning is not synonymous with that of the given word ‘indigenous’.
Option (d.), ‘native', refers to ‘characteristic of or relating to people inhabiting a region from the beginning’.
Therefore, option (d.) is correct as its meaning is synonymous to that of the given word ‘indigenous’.

Note:
If you don’t know the definition of the given word and have only used it in some given context previously, then use the given word in a sentence. Substitute the given word with each word in the options and choose the word which does not conflict with the context provided by the given word.