2. Five students need to submit their homework to the teacher on a certain day. Each student places their homework on top of the pile when they submit it, and the teacher takes the topmost homework to grade whenever they have time. The five homework submissions are numbered $1, 2, 3, 4, 5$ in the order they are submitted. By noon, it is known that the 4th homework has already been graded. Therefore, the possible order in which the teacher may grade the remaining homework in the afternoon is $\qquad$
(1) $5, 2, 3, 1$
(2) $5, 3, 2, 1$
(3) $5, 3, 1$
(4) $3, 5, 1$
2. (2)(3)(4).

If the first three assignments, 1, 2, and 3, have not been graded yet, and the 5th assignment is submitted before grading in the afternoon, then the grading situation in the afternoon will be (2);

If the 2nd assignment is graded in the morning (the teacher had time when the 2nd assignment was submitted but got busy with other tasks after grading the 2nd assignment), the grading situation in the afternoon could be (3);

If the 2nd assignment is graded in the morning, and the 3rd assignment is graded in the afternoon before the 5th assignment is submitted, then the grading situation in the afternoon could be (4).