The value of k for which the function $f(x) = \begin{cases} x^2 \sin \frac{1}{x}, & x \neq 0 \\ k(x + 1), & x = 0 \end{cases}$ is a continuous function, is : (A) $\frac{1}{4}$ (B) $2$ (C) $\frac{1}{2}$ (D) $0$