then what's difference between interface and object?
That sounds like a misunderstanding of the question. When option d says "user interface" it refers to a GUI, not an interface in the object-oriented sense.
I would agree with Michal that A, B and D appear correct.
How were you able to obtain IBM's answers to the question? When I ran through the preassessment test it only gave overall results at the end (not feedback on individual questions).