Step 1: Identify subject-verb agreement
"The teacher'' is a singular subject, so the verb should be "asks'' (not "ask'').
Step 2: Check each part
- Part A: "With a frown on his face'' — grammatically correct.
- Part B: "ask'' is incorrect; it should be "asks''.
- Part C: "to leave the room'' — perfectly fine.
Therefore, Option B contains the error.