The question I want to ask is if this is true? :-
A "HAS-A" C is true?
though C is not directly member of A though?
and another question is if anyone can tell that regarding multiple-choice questions in OCPJP 6 , the choice is given like (Choose 3(or2)) or (Choose all that apply)?
I think A "has a " C is false in your example. The implementation of B could be anything. It could change over time. It's none of A's business what is inside B.
The real exam will tell you how many answers are correct. You will not see "choose all that apply." Many study guide books use "choose all that apply" to make the questions harder. The idea is that if you can get it right in practice without knowing how many are correct, you will certainly get it right on the exam.