Writers use ___ to create a contrast between how things seem and how they really are.

Irony

Explanation:

Out of the three options, allusion, irony, and paradox, irony is the most applicable.

Irony is used when something seems the complete opposite of what one expects - "one" meaning either the character or reader. Irony can be used to contrast how things seem versus how they are because, for example, everything may seem to be going fine, but little does someone know, something's going against it the entire time.