For sets $M$ and $N$, define
$$
\begin{array}{l}
M-N=\{x \mid x \in M \text { and } x \notin N\}, \\
M \oplus N=(M-N) \cup(N-M) . \\
\text { Let } A=\left\{y \mid y=x^{2}-3 x, x \in \mathbf{R}\right\}, \\
B=\left\{y \mid y=-2^{x}, x \in \mathbf{R}\right\} .
\end{array}
$$

Then $A \oplus B=(\quad$.
(A) $\left(-\frac{9}{4}, 0\right]$
(B) $\left[-\frac{9}{4}, 0\right)$
(C) $\left(-\infty,-\frac{9}{4}\right) \cup[0,+\infty)$
(D) $\left(-\infty,-\frac{9}{4}\right) \cup(0,+\infty)$
5.C.

Let $A=\left[-\frac{9}{4},+\infty\right), B=(-\infty, 0)$, then $A \oplus B=\left(-\infty,-\frac{9}{4}\right) \cup[0,+\infty)$