Direction: Choose one word from the given options that will substitute the following expression.

An unprovoked attack by an enemy

Aggression refers to hostile or violent behavior or attitudes toward another person, which can manifest as an unprovoked attack. In military contexts, it specifically describes initiating conflict without just cause. Bootleg refers to illegal liquor, Boycott means to refuse to deal with, and Merchandise means goods for sale - none fit the context of an attack.