If $\overrightarrow a$ is a nonzero vector of magnitude $" a "$ and $λ$ a nonzero scalar, then $λ \overrightarrow a$ is unit vector if

Question

$$\begin{array} (A)\; λ = 1 \quad & (B)\; λ = -1 \quad & (C)\; a = |\; λ\; | \quad & (D)\; a = 1/|\; λ\; | \end{array}$$