Arrange the following refractory materials in ascending order of their melting points.
P. Alumina
Q. Silica
R. Carbon
S. Zirconia

A. 65 - 70% B. 45 - 50% C. 80 - 90% D. 55 - 65%

A. Up to 30 B. Up to 60 C. Up to 90 D. Up to 80

A. 5000 kcal/kg B. 8000 kcal/kg C. 7000 kcal/kg D. 9000 kcal/kg

A. 85 to 88 kcal/kg B. 850 to 880 kcal/kg C. 85000 to 88000 kcal/kg D. 8500 to 8800 kcal/kg