An alternating current is given by $I = I_0 \cos $100\pi$ t$. The least time the current takes to decrease from its maximum value to zero will be : (A) $\left(\frac{1}{200}\right)\text{ s}$ (B) $\left(\frac{1}{150}\right)\text{ s}$ (C) $\left(\frac{1}{100}\right)\text{ s}$ (D) $\left(\frac{1}{50}\right)\text{ s}$