A bucket full of hot water is kept in a room and it cools from $75^{\circ} \mathrm{C}$ to $70^{\circ} \mathrm{C}$ in $T_{1}$ minutes, from $70^{\circ} \mathrm{C}$ to $65^{\circ} \mathrm{C}$ in $T_{2}$ minutes and from $65^{\circ} \mathrm{C}$ to $60^{\circ} \mathrm{C}$ in $T_{3}$ minutes then :
(a) $T_{1}=T_{2}=T_{3}$
(b) $T_{1}<T_{2}<T_{3}$
(c) $T_{1}>T_{2}>T_{3}$
(d) $T_{1}<T_{2}>T_{3}$