Answer:
The answer to your question would be that the sentence that contains an unnecessary shift in verb tense is the following one: Lee noticed a problem and alerts a teacher.
Step-by-step explanation:
In the sentence above, the first verb phrase is in the past simple tense and the second one is in the present simple tense. The fact is that the verb tense expresses a sense of time in a sentence, paragraph, or paper. The writer should establish the time perspective in the opening sentence and maintain that tense consistently throughout his or her work. As I've said, the time reference is not maintained within the sentence in question. Consequently, this may cause distractions to the reader and a break in coherence. Therefore, the sentence should be as follows: Lee noticed a problem and alerted a teacher.