Dear Mooli,
Question 1: The reason is you have to take all the project constraints, not just the triple constraints. The choice 3 is more suitable for the steps to take regarding the change control.
Question 2: I would think to pick the choice 3 for this answer, only if the phrase "before taking a decision" is not mentioned in the answer choice. This phrase is telling me that you are skipping the change control process. Of course, whenever you have a client or customer asking for a change, you always assess the impact on the project constraints.
Where do you get these questions from? I would suggest you check out Rita's change control steps where she gives steps by steps on the change control.