In the context of a student investigating the relationship between temperature and kinetic energy in one phase of matter (assuming we're discussing gases or liquids), the graph would typically show a direct proportional relationship. As the temperature increases, the kinetic energy of the particles also increases.
Therefore, the graph would most appropriately be a diagonal line that slopes upwards to the right, indicating that as temperature increases, kinetic energy increases.
So, the correct response is a diagonal line.