The temperature of a pendulum, the time period of which is $t$, is raised by $\Delta T$. The change in its time period 15:
(a) $\frac{\overline{1}}{2} \alpha f \Delta T$
(b) $2 \alpha t \Delta T$
(c) $\frac{1}{2} \alpha \Delta T$
(d) $2 \alpha \Delta T$