Which function allows an administrator to quickly add multiple members in ArcGIS Online?

The option indicating that administrators can add members without sending invitations in a streamlined bulk process is correct because ArcGIS Online offers a feature specifically designed to enhance the efficiency of managing users. This function allows administrators to upload a list of members, circumventing the need for individual invitations. By using this method, administrators can efficiently manage user accounts, especially in situations where a large number of users need to be added simultaneously.

This bulk process is particularly beneficial for organizations that are onboarding multiple users at once or making significant changes to their member list, as it saves time and reduces administrative overhead. It also ensures that the new members are added directly to the organization, making them readily available to access the resources they need without going through the delays associated with invitation-based processes.

The other options may seem beneficial but are not as efficient or streamlined for bulk actions. For instance, adding members using email addresses or copying usernames from a file entails more manual steps and does not leverage the convenience of a bulk addition feature. Additionally, inviting members using a single method still requires sending invitations and waiting for acceptance, which is not as immediate as direct addition without invitations.