Final answer:
The sentence 'At the end of the first semester.' is a sentence fragment, lacking a subject and a verb to form a complete thought. The error corresponds to option 'e. fragment'.
Step-by-step explanation:
The sentence 'At the end of the first semester.' is an example of a sentence fragment because it lacks both a subject and a verb required to form a complete thought. To correct this error, the sentence must be revised to include a main clause that states what happened at the end of the first semester, providing the necessary subject and verb. For example, it could be corrected to 'The first semester ended with high grades for many students,' which now makes it a complete sentence.
To answer the original question, the error in the sentence 'At the end of the first semester.' is that it is a fragment.