The correct answer is D. To inform
Explanation:
In writing, the purpose of a sentence, paragraph or text refers to the reason for writing a text and this can be identified according to the type of content they include. Common purposes in writing include to persuade that aims at convincing the audience of an idea or perspective; to entertain that aims at entertaining the audience; to narrate that aims at telling a set of events and to inform that aims at providing information about one topic or subject.
In the case of the sentence "All living things are composed of cells" this sentence is mainly an objective sentence that provides information in the field of biology about living beings and therefore the purpose of this sentence is to inform as it is just providing information rather than entertaining, narrating a story or trying to convince the audience.
