Ans: D
Let $m$ be the slope of the required straight line.
Let $m$ be the slope of the required straight line.
Note that the slope of the straight line $x+2y+3=0$ is $-\dfrac{1}{2}$.
Since the two straight lines are perpendicular to each other, we have
$\begin{array}{rcl}
m & = & -1 \div -\dfrac{1}{2} \\
m & = & 2
\end{array}$
Therefore, the equation of the required straight line is
$\begin{array}{rcl}
y-3 & = & 2(x-1) \\
y-3 & = & 2x-2 \\
2x-y+1 & = & 0
\end{array}$
