[填空题]
How long does it take the Sun to melt a b2bgey,q hum ,(j z5f6il(zh9f lb;lqq1,hr3 l qock of ice at 0$^{\circ} C$ with a flat horizontal area $1.0\,m^2$ and thickness 1.0 cm? Assume that the Sun’s rays make an angle of 30$^{\circ} $ with the vertical and that the emissivity of ice is 0.050. h