A writer might choose to write in third person primarily for option C: To allow the narrator to speak in a voice that is different from the character's.
Third-person narration provides the writer with the flexibility to convey multiple characters' thoughts, emotions, and actions, as well as to create a distinct narrative voice that may differ significantly from any individual character's perspective. This can help provide a more objective viewpoint or offer insights into the story that a first-person perspective might not allow.
Other options, like A, B, and D, might be specific effects that can also be achieved through different narrative techniques, but they are not inherent to the third-person perspective itself.