Correct Answer: C
Explanation:
The timeline of this sentence is off. The first phrase is in the past tense, so the verb “has taught” needs to indicate that it happened before that point in the past. So, "has taught" should be changed to "had taught," and "has taught" contains the sentence's error. The corrected sentence reads, "Long before she began her tenure as chair of the Biology department, Professor Zarina had taught undergraduate classes in Punjabi literature."