Choice A is the best answer. In lines 85-86("Will...cale") the author asks, "Will companies be able to boost their products by manipulating online ratings on a massive scale?" In the context of selling products by manipulating user reviews on a massive scale, the word "scale" most nearly means level or size.
Choices B, C, and D are incorrect because in the context of selling products by manipulating user reviews, a massive "scale" refers to a great level or size, not to a payment (choice B), an interval or space between things (choice C), or a plan (choice D).