Explanation
Correct answer: D.
Choice D is the best answer because it most logically completes the text’s discussion of the W boson. In this context, "scale" means size or extent. The text indicates that recent measurements of the W boson were remarkable because they revealed the subatomic particle’s mass to be much greater ("seven standard deviations higher") than had been expected based on a standard model. This context conveys not only that the measurements differed from predictions but also that the extent of the difference was very large.
Why the other choices are wrong
Choice A
Choice A is incorrect. Although the text indicates that there was a very large difference between the predicted mass and the actual measured mass of the subatomic particle, it doesn’t explain the cause of, or reason behind, that difference.
Choice B
Choice B is incorrect because it wouldn’t make sense to say that the measurements of the subatomic particle were notable because they differed from expectations and also because a difference existed between the measurements and what had been predicted; the text would be repeating the idea that there was a difference instead of adding to that idea.
Choice C
Choice C is incorrect because the text doesn’t convey any implications of, or consequences of or conclusions drawn from, the fact that the mass of the subatomic particle differed from expectations; the context indicates only that the actual measured mass was much higher than the predicted mass.