问题
已知积分路径 $L$ $=$ $L_{1}$ $+$ $L_{2}$, 则根据第一类曲线积分中积分路径的可加性,以下选项中,正确的是哪个?选项
[A]. $\int_{L}$ $f(x, y)$ $\mathrm{d} s$ $=$ $\int_{L – L_{1}}$ $f(x, y)$ $\mathrm{d} s$ $+$ $\int_{L – L_{2}}$ $f(x, y)$ $\mathrm{d} s$[B]. $\int_{L}$ $f(x, y)$ $\mathrm{d} s$ $=$ $\int_{L_{1}}$ $f(x, y)$ $\mathrm{d} s$ $-$ $\int_{L_{2}}$ $f(x, y)$ $\mathrm{d} s$
[C]. $\int_{L}$ $f(x, y)$ $\mathrm{d} s$ $=$ $\int_{L_{1}}$ $f(x, y)$ $\mathrm{d} s$ $+$ $\int_{L_{2}}$ $f(x, y)$ $\mathrm{d} s$
[D]. $\int_{L}$ $f(x, y)$ $\mathrm{d} s$ $=$ $\int_{\frac{L_{1}}{2}}$ $f(x, y)$ $\mathrm{d} s$ $+$ $\int_{\frac{L_{2}}{2}}$ $f(x, y)$ $\mathrm{d} s$