问题
已知第二类曲线积分中的积分路径 $L$ 为有向曲线弧，$L^{-}$ 为与 $L$ 方向相反的曲线，则，当积分路径分别为 $L$ 和 $L^{-}$ 时，以下等式所对应的转换关系正确的是哪个？选项
[A]. $\begin{cases} \int_{L} P(x, y) \mathrm{d} x=-\int_{\frac{1}{L^{-}}} P(x, y) \mathrm{d} x, \\ \int_{L} Q(x, y) \mathrm{d} y=-\int_{\frac{1}{L^{-}}} Q(x, y) \mathrm{d} y. \end{cases}$[B]. $\begin{cases} \int_{L} P(x, y) \mathrm{d} x=\int_{L^{-}} P(x, y) \mathrm{d} x, \\ \int_{L} Q(x, y) \mathrm{d} y=\int_{L^{-}} Q(x, y) \mathrm{d} y. \end{cases}$
[C]. $\begin{cases} \int_{L} P(x, y) \mathrm{d} x=-\int_{L^{-}} P(x, y) \mathrm{d} x, \\ \int_{L} Q(x, y) \mathrm{d} y=-\int_{L^{-}} Q(x, y) \mathrm{d} y. \end{cases}$
[D]. $\begin{cases} \int_{L} P(x, y) \mathrm{d} x=\frac{1}{\int_{L^{-}} P(x, y) \mathrm{d} x}, \\ \int_{L} Q(x, y) \mathrm{d} y=\frac{1}{\int_{L^{-}} Q(x, y) \mathrm{d} y}. \end{cases}$
$\begin{cases} \int_{L} P(x, y) \mathrm{d} x=-\int_{L^{-}} P(x, y) \mathrm{d} x, \\ \int_{L} Q(x, y) \mathrm{d} y=-\int_{L^{-}} Q(x, y) \mathrm{d} y. \end{cases}$