Until the day is over. After the instructor had marked them up and graded them. Another clue is that the word group begins with a relative pronoun. Whom Kelly had known since the third grade. Pointing out these structures in literature read and written in class might be a good way to identify the difference between strong use of sentence fragments and weak sentence fragments.
Every life is many days, day after day.
But always meeting ourselves. A sentence fragment is used here for emphasis. In this example, the meaning of the fragment is clear. It is very easy to misuse sentence fragments. As is shown in the following piece of writing, this will make the writing unclear and disorganized.