The radiant energy from the sun incident normally at the surface of earth is \[20\ kcal/{{m}^{2}}min\]. What would have been the radiant energy incident normally on the earth, if the sun had a temperature twice of the present one [CBSE PMT 1998; Pb. PET 2001]

• A.            \[160\ kcal/{{m}^{2}}\ min\] 
• B.            \[40\ kcal/{{m}^{2}}\ min\]
• C.            \[320\ kcal/{{m}^{2}}\ min\] 
• D.            \[80\ kcal/{{m}^{2}}\ min\]