Example 10 (2003 National High School Competition Question) Let $a, b \in \mathbf{R}, ab \neq 0$. Then, the graph of the line $ax-y+b=0$ and the curve $bx^2+ay^2=ab$ is ( ).
A
B
C
D
Solution: Choose B. Reason: The equation of the straight line can be written as $y=a x+b$, and the equation of the curve can be written as $\frac{x^{2}}{a}+\frac{y^{2}}{b}=1$. If $a0$, then it contradicts A, B, and C; if $a>0, b>0$, then it also contradicts A, B, and C; when $a>0, b<0$, only B is consistent.