Which fits in the group of RAP, MAP, HOT FUN ?

Option D

a, e, i, o, u are vowels and there is a vowel consonant relationship in every group of the series. So, CAT fits in the group of RAP, MAP, HOT FUN. 

Detailed explanation:

In each word or phrase in the group (RAP, MAP, HOT FUN), there is a consistent pattern of vowels and consonants:

• RAP: Consonant-Vowel-Consonant
• MAP: Consonant-Vowel-Consonant
• HOT FUN: Consonant-Vowel-Consonant Consonant-Vowel-Consonant
• CAT (option D): Consonant-Vowel-Consonant (follows the pattern in the question)

CAT fits this pattern, while the other options (HNE, PGI, STN) do not.