What is $( - 1)^1 + ( - 1)^2 + \cdots + ( - 1)^{2006}$?
$\text {(A) } - 2006 \qquad \text {(B) } - 1 \qquad \text {(C) } 0 \qquad \text {(D) } 1 \qquad \text {(E) } 2006$
$(-1)^n=1$ if n is even and $-1$ if n is odd. So we have
$-1+1-1+1-\cdots-1+1=0+0+\cdots+0+0=0 \Rightarrow \text{(C)}$