Final answer:
The ABN must be printed using at least 12-point font size and in dark ink to ensure legibility and clarity on official documents.
Step-by-step explanation:
The ABN (Australian Business Number) must adhere to specific guidelines to ensure clarity and legality in documentation. These guidelines are not related to the use of italics but pertain to the visibility and legibility of the number itself. The correct answer to what the ABN must have is D. both A and B. This means that the ABN should use at least 12-point font size and must be in dark ink. These requirements are designed to ensure that the ABN can be read easily on any legal or official document where it is displayed. Legibility is crucial to prevent any misinterpretation or error in handling business identification.