SampleDomain.cs

public class ConcreteEntityA : ActivatableEntity
{
    //...
}

public class ConcreteEntityB : ActivatableEntity, AuditEntity //not possible!!!
{
    //...
}

public class AuditEntity : EntityBase
{
    DateTime CreatedOn { get; set; }
    DateTime ModifiedOn { get; set; }
}

public class ActivatableEntity : EntityBase
{
    public bool IsActive { get; set; }
        
    public void Active()
    {
        //...   
    }

    public void DeActivate()
    {
        //...   
    }
}