Ans: D
According to the slope-intercept form, the slope and the $y$ intercept of $L_1$ are $a$ and $b$ respectively, and the slope and the $y$ intercept of $L_2$ are $c$ and $d$ respectively. According to the given figure, $a>0$, $b<0$, $c<0$ and $d>0$.
According to the slope-intercept form, the slope and the $y$ intercept of $L_1$ are $a$ and $b$ respectively, and the slope and the $y$ intercept of $L_2$ are $c$ and $d$ respectively. According to the given figure, $a>0$, $b<0$, $c<0$ and $d>0$.
A must be false. Since $a>0$ and $b<0$, then $ab<0$.
B must be false. Since $c<0$ and $d>0$, then $cd<0$.
C cannot be justified to be true or false.
D must be true. Since the intersection point lies on the positive $x$-axis, then the $y$ coordinate of the intersection is $0$. Sub. $y=0$ into the equation of $L_1$, we have
$\begin{array}{rcl}
0 & = & ax + b \\
x & = & \dfrac{-b}{a}
\end{array}$
Sub. $y=0$ into the equation of $L_2$, we have
$\begin{array}{rcl}
0 & = & cx + d \\
x & = & \dfrac{-d}{c}
\end{array}$
Hence, we have
$\begin{array}{rcl}
\dfrac{-b}{a} & = & \dfrac{-d}{c} \\
ad & = & bc
\end{array}$
