ব্যাখ্যা
The correct answer is option (a) "adjective."
'Fatherly' is an adjective meaning resembling or characteristic of a father; showing paternal kindness.
Example: 'He gave me some fatherly advice.'
Note: Although 'fatherly' ends in '-ly' (which usually makes adverbs), it is an adjective here. Other '-ly' adjectives: lovely, friendly, timely, elderly, cowardly.
Source: Oxford English Dictionary.