Ans: B
By the remainder theorem, we have
By the remainder theorem, we have
$\begin{array}{rcl}
f(-k) & = & k \\
(-k)^3 +k(-k)^2 +2k(-k) +3k & = & k \\
-k^3 + k^3 -2k^2 +2k & = & 0 \\
k^2 – k & = & 0 \\
k(k-1) & = & 0
\end{array}$
$\therefore k=0$ or $k=1$.
Note that $k$ is a non-zero constant, then $k=1$.
