Ans: D
I is false. According to the figure, the graph opens downwards. Therefore, $a < 0$.
I is false. According to the figure, the graph opens downwards. Therefore, $a < 0$.
II is true. According to the figure, the $y$ intercept of the graph is negative. Therefore, $b < 0$.
III is true. According to the figure, the graph has two distinct real roots. Therefore, $\Delta > 0$. Hence, we have
$\begin{array}{rcl}
(-2)^2-4(a)(b) & > & 0 \\
4-4ab & > & 0 \\
4 & > & 4ab \\
ab & < & 1
\end{array}$
