For the reaction $2A + B \to \text{Product}$,the rate law is given as $\frac{-d[A]}{dt} = K[A]$. At a time when $t = \frac{1}{K}$,the concentration of the reactant $A$ is ($Co =$ initial concentration).

• A
  $\frac{Co}{e}$
• B
  $Co \,e$
• C
  $\frac{Co}{e^2}$
• D
  $\frac{1}{Co}$