|A) Surprisingly||B) Happily|
|C) Arrogant||D) Humble|
Here the given words Careful and Cautious are related in such a way that they are Synonyms of each other.
Therefore, Similarly Boastful is synonym to the word Arrogant.
Happily and Humble are Antonyms of Boastful and Surprisingly is the word not related to Boastful in any way.
So, Careful is to Cautious as Boastful is to Arrogant.