What statement best characterizes the standard structure of creating game design documents?

There is no standard way of creating a game design document.
There are a number of formats for creating game design documents, but one must be chosen.
There is a standard way of creating a game design document, but changes can be made.
There is a strict standard way for creating game design documents.

The game design document is like a Software Requirement Specification, and it is developed with the agreement of the designer, artist, and programmer. Its main aim is to unambiguously explain the selling points, gameplay, level design, art, target audience, story, UI, assets, characters, etc.. And in brief each of the game parts that need development must be included by the developer in a detailed way for the concerned developer to get a clear picture of it before implementing. And the document is sectioned for clarity as well as segmented in a manner in which the game developer can look at any time for reference, and maintain the relevant parts.

Various important sections are: Story, characters, environment/level design

Art, Gameplay, User Interface, Game Controls, Sound and Music, Monetization, and Accessibility. This list is not exhaustive and applies to all games. However, some of the segments might not be a part of the GDD but they will certainly be a part of the supplementary documents.

Thus, the option mentioned in the answer section is the correct option.