Ans: A
$\left\{ \begin{array}{ll}
p+3q = 4 & \ldots \unicode{x2460} \\
5p+9q = 2 & \ldots \unicode{x2461}
\end{array} \right.$
$\left\{ \begin{array}{ll}
p+3q = 4 & \ldots \unicode{x2460} \\
5p+9q = 2 & \ldots \unicode{x2461}
\end{array} \right.$
$\unicode{x2460} \times 3$, we have
$\begin{array}{rcl}
3p + 9q & = & 12 \ \ldots \unicode{x2462}
\end{array}$
$\unicode{x2461} – \unicode{x2462}$, we have
$\begin{array}{rcl}
2p & = & -10 \\
p & = & -5
\end{array}$
