I understand you're looking for an article about an answer key or guide for a "Grammar and Usage Set B" PDF. However, I don’t have access to specific third-party PDF files or their answer keys (e.g., from a particular textbook, workbook, or exam prep series like Set B ).
Instead, I can offer you a that explains how to approach grammar and usage questions of the kind typically found in such a "Set B" exercise, along with a self-check answer key you can use for practice.