If rotation of the earth stopped suddenly then the rise in temperature of the earth, assume total rotational energy is converted into thermal energy, is: (specific heat of earth $=0.15$, radius of earth $=6400 \mathrm{~km}$ )
(a) $78.76^{\circ} \mathrm{C}$
(b) $6.876^{\circ} \mathrm{C}$
(c) $68.76^{\circ} \mathrm{C}$
(d) $0.6876^{\circ} \mathrm{C}$