Option 1: (B), (C), (D), (A) -> Creates a disjointed sentence with improper flow and unclear meaning.
Option 2: (C), (A), (B), (D) -> Results in incomplete structure with "until the" left hanging at the end without proper conclusion.
Option 3: (B), (A), (D), (C) -> Produces a grammatically incorrect sentence with "although" awkwardly placed at the end.
Option 4: (C), (B), (D), (A) -> Forms the complete sentence: "Although the professor explained the complex theories in great detail, the students struggled to grasp the underlying concepts until the practical demonstration clarified their doubts" - grammatically correct with proper logical flow.
Hence, Option 4: (C), (B), (D), (A) -> This arrangement creates a coherent complex sentence that begins with a dependent clause ("Although..."), shows contrast between theoretical explanation and practical understanding, and concludes with the resolution that clarified the students' doubts -> correct