3. Ed liked the teacher because she did not (condescend) to the student.
Explanation:
This is the only example that uses the correct form of the underlined word. In this case, the author wants to use a verb, as he is talking about what the teacher did not do. "Condescend" is indeed a verb. Moreover, the word is used in the correct tense (simple past) and the correct person. Therefore, the sentence is understandable.