Select all correct answers regarding DOI $($digital object identifier$)$ and URL $($universal reference link$)$:

Include the DOI for all works that have a DOI, regardless of whether you used the online version or the print version.

If a print work does not have a DOI, do not include anu DOI or URL in the reference.

If an online work has both a DOI and a URL, include only the DOI.

If an online work has a URL but no DOI, include the URL in the reference.