If the permissible compressive and tensile stresses in a singly reinforced beam are 50 kg/cm2 and 1400 kg/cm2 respectively and the modular ratio is 18, the percentage area At of the steel required for an economic section, is__________________?
A. 0.496 %
B. 0.596 %
C. 0.696 %
D. 0.796 %