to do 与 doing

题目

to do 与 doing
Turning to the left,you'll find the post office.可不可以写成To turn to the left,you'll find the post office.
为什么?
那语法上有没有错？

答案

这句是分词作状语的句式,意思是:When you turn to the left,you'll find the post office.
如果用的是 To turn to the left ,表示的是目的,意思不对