How many users can work on a scheme sheet at the same time?

In many design and engineering software applications, a scheme sheet typically allows for only one user to work on it at a time. This limitation stems from the need to maintain data integrity and prevent conflicts that could arise if multiple users try to edit the same content simultaneously. When more than one user accesses the same document concurrently, there is a significant risk of overwriting changes or creating inconsistencies, which would compromise the accuracy of the project or design.

Therefore, the correct answer reflects the standard practice of having a single user manage and edit the scheme sheet to ensure that all modifications are made in an orderly manner and that the version control remains clear. This enhances collaboration in a team environment by allowing users to take turns editing and reviewing rather than competing for access to the same document simultaneously.