Select the most appropriate option to fill in the blanks.
_____ Amazon rainforest is the largest rainforest in _____ world.

Correct option is A

The correct option to fill in the blank is (a) The; the.

Explanation:
'The' is used before the names of unique geographical features like 'Amazon rainforest'. Similarly, 'the' is used before 'world' because there is only one world (unique object).

Example: The Nile is the longest river in the world.

Information Booster:
Definite article 'the' is mandatory before superlative adjectives (the largest) and unique entities (the sun, the moon, the world).

So the correct answer is (a)