设函数z=ln(x^2+y^2)，则dzbigg|(1,-2)=(）A. (4)/(5)dx+(1)/(5)dyB. (1)/(5)dx+(2)/(5)dyC. (2)/(5)dx-(4)/(5)dyD. (4)/(5)dx+(2)/(5)dy

设函数$z=\ln(x^2+y^2)$，则$dz\bigg|(1,-2)=$(）

A. $\frac{4}{5}dx+\frac{1}{5}dy$

B. $\frac{1}{5}dx+\frac{2}{5}dy$

C. $\frac{2}{5}dx-\frac{4}{5}dy$

D. $\frac{4}{5}dx+\frac{2}{5}dy$