What defines an object diagram's compliance with class diagram

[larrylawl]

(Lecture 3 Post Lecture Quiz, Q19)
I understand the given reason. However, isn't there a missing association between Student and Admin objects? My larger question is: what defines an object diagram's compliance with class diagram.

[damithc]

As the class diagram does not specify multiplicities, we can't say that there must be an association between Admin and Student objects.
An OD is compliant with a CD as long as the OD could be an instance of the CD (i.e., it is an object structure that could have been resulted from a system that implements the CD). In other words, the OD does not violate any part of the CD.

[larrylawl]

Got it, thanks prof!