Answer:
Ms. Morris has to form 5-students groups.
Explanation:
If Ms. Morris wants to divide all 25 students in 3, 4 or 5 equal teams, she to apply a division to know the number of students per group.
If she makes 3-students groups, it would be

Ms. Morris can't make 3-students groups, because she cant divide one student in parts to have equal groups.
If she considers 4-students groups, it would be

The same reason here, she cannot divide a students in parts to have equal groups.
Therefore, she has to make 5-students groups, because

Which means she can make groups of 5 students each, and she would have equal groups.