Hi Vivian! Thanks for your question, and happy to help you out with understanding this
Let's look for some support for the idea that Eltis questioned Williams' analysis. First, we need to understand what Williams' analysis was, which is described in the first paragraph. Williams argued that British abolition and emancipation were driven primarily by economic motives: depleted soil, indebtedness, and the inefficiency of coerced labor.
Eltis' view is described in the third and fourth paragraphs. More specifically, paragraph 4 explains how Eltis challenges Williams' analysis: Eltis argued that Williams "underestimated the economic viablity of the British colonies employing forced labor" even though Williams' insights about economic motives were partially correct, as well as that reasons other than the ones cited by Williams were responsible for convincing British leaders that free labor was more beneficial to the economy. Since Eltis describes how Williams "underestimated" certain factors and cited different reasons than Williams did, we can conclude that he "questioned Williams' analysis." These same lines also help support the idea that there is support for part of Williams' conclusion, since they tell us that his insights were "partly accurate."
Let's also look at why answer choice (A) is wrong. The reason answer choice (A) is wrong is that the passage does not say that Eltis believes that moral persuasion by abolitionists was a significant factor in Britain's abolition of slavery. Since the passage does not say that Eltis believes this, answer choice (A) cannot be correct.
Additionally, answer choice (B) accurately captures what the main point of the passage is: the passage describes the work of two scholars that reexamined Williams' conclusion about Britain's abolition of slavery and how this work demonstrates that there is support for part of Williams' conclusion. By contrast, answer choice (A) does not capture the idea that the passage aims to examine these Drescher's and Eltis' work in the context of the work done by Williams.
I hope this helps, and please let me know if you have any other questions!