A sphere of density p, specific heat capacity c and radius r is hung by a thermally insulating thread in an enclosure which is kept at a lower temperature than the sphere. The temperature of the sphere starts to drop at a rate which depends upon the temperature difference between the sphere and the enclosure and the nature of the surface of sphere and is proportional to

• A. \[\frac{c}{{{r}^{3}}\rho }\]
• B. \[\frac{1}{{{r}^{3}}\rho c}\]
• C. \[3{{r}^{3}}\rho c\]
• D. \[\frac{1}{r\rho c}\]