It's ABD.

A,B,C is the correct answer

A and B are clear.
C is correct cause in the salesforce docs you can see this afirmation: 'You can’t add a method to a global interface after the class has been uploaded in a Managed - Released package version'
Specifically, it talks about global interfaces not public, so I think C is correct (more even because D and E are not correct)

D is false because an interface cannot be private as Radar said.
E is false because an interface only contains the method signatures, no the implementation

Interface have no access modifiers. they are always global

interface cannot be Private, D is not correct

A,B,D is the correct answer