Answer:
Imperative
Step-by-step explanation:
An imperative sentence is one that gives an order or asks for the other person to perform some action. This is the case with this sentence, as the speaker is "ordering" the listener to turn on his headlights when his windshield wipers are running.
An exclamatory sentence is one that is uttered with excitement or in a passionate way. These are usually followed by an exclamation point. An interrogative sentence is one that asks a question and is followed by a question mark. Finally, a declarative sentence is one that states a point or remarks on a fact.