Yes, I would consider myself smart.
Hooke's law: The extension is proportional to the force acting(constant is positive). As Y is the only one with a positive constant gradient, it is the only one that obeys Hooke's law.
I don't do EdExcel, but in general think logically about the question. For physics, you will usually get all of the marks if you progress through the correct points with enough detail. Do past papers and practice these questions.
Are these questions that you struggle with usually explanation-based or calculation-based? If calculation-based, do you maths? If so, do you do M1?