Answer: Declarative Sentence because it is a statement or an opinion, which always ends in period. It isn't Interrogative because they end with a question mark, and not Imperative because it is a command or request and ends usually with a period, but sometimes an exclamation mark.
Examples for an Interrogative Sentence:
“When are you going to turn in your writing assignment?”
“Do you know what the weather will be tomorrow?”
Examples for an Imperative Sentence:
“Please sit down.”
“I need you to sit down now!”