Ans: D
From the equation $x+ay+b=0$, we have
From the equation $x+ay+b=0$, we have
$\begin{array}{rcl}
\text{the slope} & = & -\dfrac{1}{a} \\
\text{the $y$-intercept} & = & -\dfrac{b}{a}
\end{array}$
I is true. From the graph, the slope is positive. Then we have
$\begin{array}{rcl}
-\dfrac{1}{a} & > & 0 \\
a & < & 0
\end{array}$
II is true. From the graph, the $y$-intercept is negative. Then we have
$\begin{array}{rcl}
-\dfrac{b}{a} & < & 0 \\
b & < & 0
\end{array}$
III is true. From the graph, the $y$-intercept is larger than $-1$. Then we have
$\begin{array}{rcl}
-\dfrac{b}{a} & > & -1 \\
\dfrac{b}{a} & < & 1 \\
b & > & a \\
a & < & b
\end{array}$
