when the finished planting trees,they were very happy 有错么

问题描述:

when the finished planting trees,they were very happy 有错么
是说昨天学生们去种树的一篇英语作文 这个句子有错么?如果有错改怎么改
打错了昰when they……

在finished前加had,表示他们已经种完树.