复数z满足：（3﹣4i）z=1+2i，则z=（   ）

A：$-\frac{1}{5}+\frac{2}{5}i$

B：$\frac{1}{5}-\frac{2}{5}i$

C：$-\frac{1}{5}-\frac{2}{5}i$

D：$\frac{1}{5}+\frac{2}{5}i$