The companies with a proportional relationship between the number of minutes and the monthly cost are Nation Mobile and Cellular Prime.
In this question, we are comparing the number of minutes per month and the monthly cost for three cell phone companies: Mobile Plus, Cellular Prime, and Nation Mobile.
To determine if there is a proportional relationship between the number of minutes and the monthly cost, we need to check if the ratio of minutes to cost remains constant.
By examining the table, we can see that the ratio of minutes to cost is the same for Cellular Prime and Nation Mobile. Therefore, the answer is C. Nation Mobile and Cellular Prime.