The correct answer is B. A statement
Step-by-step explanation:
In writing a theme is defined as the main underlying idea that covers all the text, this main idea can be stated implicitly or explicitly depending on the type of text and level of formality, for example in case of stories the theme is not explicitly stated, but in other such as articles it is. As this is the idea that guides a text, it is important to use a statement to make the theme clear, this means the theme should be expressed in an affirmative, clear and concise sentence, this also implies the theme cannot be summarized with only one word and a question or exclamation should not be used. Thus, a theme is best written as a statement.