Choose the most appropriate conjunction to fill in the following sentence _______ he worked hard enough he could not pass the exam

"Although" indicates contrast fitting the context of working hard but failing making option D correct. Other options are incorrect. Proper conjunction usage ensures clarity especially in narrative or analytical writing. This skill is vital for professional communication. Accurate conjunctions convey relationships effectively particularly in essays or reports where precise language enhances clarity and impact in describing contrasts or outcomes in various contexts.