$(1+x^2)(1-x^3)$ equals
$\text{(A)}\ 1 - x^5\qquad \text{(B)}\ 1 - x^6\qquad \text{(C)}\ 1+ x^2 -x^3\qquad \\  \text{(D)}\ 1+x^2-x^3-x^5\qquad \text{(E)}\ 1+x^2-x^3-x^6$
We multiply: $(1+x^2)(1-x^3) = 1 - x^3 + x^2 - x^5$. Thus the answer is $\boxed{D}$.
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