Once the balance of nature is disturbed,it is.
问题描述：
Once the balance of nature is disturbed,it is.
这里为什么不填非谓语形式disturbrd?
答
可以成为非谓语形式的：
Once disturbed,the balance of nature is likely to take at least 25 years to restore.
--------这里,Once disturbed 就是非谓语形式,代替时间状语从句Once the balance of nature is disturbed.