Option 1 -> lucid means clear and easy to understand, which would help students comprehend, not leave them confused.
Option 2 -> ambiguous means unclear or open to multiple interpretations, which would cause confusion.
Option 3 -> straightforward means direct and easy to follow, which would prevent confusion.
Option 4 -> Enlightening means informative and clarifying, which would eliminate confusion.
Hence, Option 2: ambiguous -> The sentence indicates a cause-effect relationship where the professor's explanations led to student confusion. Only "ambiguous" (unclear, vague, or having multiple meanings) logically explains why students remained confused despite receiving explanations -> correct