One of the factors of $x^4+4$ is: 
$\textbf{(A)}\ x^2+2 \qquad \textbf{(B)}\ x+1 \qquad \textbf{(C)}\ x^2-2x+2 \qquad \textbf{(D)}\ x^2-4\\  \textbf{(E)}\ \text{none of these}$
$(x^2-2x+2)\cdot(x^2+2x+2)=x^4+4 \implies \textbf{(C)}$