设 $L_{1}: x^{2}+y^{2}=1, L_{2}: x^{2}+y^{2}=2, L_{3}: x^{2}+2 y^{2}=2, L_{4}: 2 x^{2}+y^{2}=2$ 为四条逆时针方向的平面曲线. 记 $I_{i}=\oint_{L_{i}}\left(y+\frac{y^{3}}{6}\right) \mathrm{d} x+\left(2 x-\frac{x^{3}}{3}\right) \mathrm{d} y(i=1,2,3,4)$, 则 $\max \left\{I_{1}, I_{2}, I_{3}, I_{4}\right\}=(\quad)$
性质，看图解
$\text{A.}$ $I_{1}$.
$\text{B.}$ $I_{2}$.
$\text{C.}$ $I_{3}$.
$\text{D.}$ $I_{4}$.