The correct answer is C. Is doing
Explanation:
In the English language, the present participle is a form verb that ends in "-ing" and can be used in the present, past or future as part of continuous tenses that describe actions that are continuous in time or as adjectives to modify nouns. This implies in the case of the sentence "She _____ what she was told to do" the only option that contains a present participle is "is doing" as this includes the verb "do" followed by "-ing" along with the auxiliary verb "is" that creates a continuous tense in present and completes the sentence.
