Final answer:
A period is the correct punctuation mark to place at the end of a declarative or imperative sentence.
Step-by-step explanation:
A period should be placed at the end of each statement. This punctuation mark is used to end declarative (statement) and imperative (command) sentences, such as 'The administration canceled classes.' Periods are vital in writing for clarifying the end of a sentence and separate it from the following sentence.