Answer:
B, You have to be cruel to be kind
Explanation:
<em>A paradox is a statement that seems self-contradictory on the surface but, upon closer inspection, actually rings true. </em>
In this example, at first thought, being cruel is never kind, but if you think more deeply about it you realize that is can be true. Tough love is one use of this, as parents sometimes have to be strict and/or mean (perform a cruel action) in order to teach their children right from wrong. (perform a kind action)
A is an oxymoron. "Awfully" and "pretty" are contradictory terms.
C is verbal irony. You wouldn't expect something so large to be called tiny.
D is alliteration. Dark, dim, and doorway all start with the same sound.