Select the most appropriate option to fill in the blanks.
_______ it seemed improbable, he learned from his students _______ he was teaching.

Correct option is D

The correct option to fill in the blank is (D) Although; while.

Explanation: 'Although' is a conjunction used to introduce a concessive clause, indicating a contrast (it seemed improbable, yet it happened). 'While' is used to indicate that two actions are happening simultaneously (learning and teaching).

Example: Although it was raining, he went for a walk while listening to music.

Information Booster: 'Although' sets up a contrast, and 'while' establishes a temporal relationship. This combination makes the sentence logically coherent.

So the correct answer is (d)