The answer key is " A"
Anyway, I and most of my friends agree with D but we change our minds after reading the explanation.
From question, there is a relationship of 3 technical terms
Cost ---(Increased by X%)---->Asking Price----(Decreased by Y%)---->Selling Price.
From (2), we know only Selling Price but not Asking Price. Therefore, we cannot find the Cost. The tricky point is that Asking Price is not always Selling Price.
Any idea from its explanation?
Exceed your goals and then Proceed to Succeed!!