2.1.3 Maple

A grade: { 1, 2, 3, 4, 5, 6, 7, 8, 21, 22, 24, 26, 27, 29, 31 }

B grade: { 9, 10, 11, 13, 14, 28 }

C grade: { 12, 15, 16, 17, 18, 19, 20, 23, 30 }

F grade: { 25 }