Paragraph blocks are especially useful in problem-and-solution essays because they allow a writer to a track the use of transitional phrases to ensure clarity b expand on solutions that have failed in the past c explain ideas as they occur to him or her d explain a problem at length and identify components to a solution

D). Explain a problem at length and identify components to a solution.

Explanation:

An essay is described as the 'exploration of ideas' that intends to propose a detailed analysis and elaboration of a specific along with the author's concluding remarks. As far as a problem-and-solution essay is exemplified as the essay that recognizes a problem/issue and proposes solutions to solve that problem with an aim to instruct and persuade the readers to implement the strategy or action plan(solutions) proposed by the author.

As per the question, the paragraph blocks in such essays are beneficial as it permits the author to 'detail a problem at length and identify the components to a solution' and then attempts to convince the audience to believe in the regimen proposed to resolve the problem. Thus, option D is the correct answer.