Multiple choice general knowledge

My new colleague is a bit of a rough________but i think i'm going to like him once i get used to him

  1. stone

  2. rock

  3. diamond

  4. pearl

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The idiom is rough diamond, someone who appears unpolished or uncultured but has good qualities underneath. Option C is correct. Rough stone, rough rock, and rough pearl are not standard idioms.