说明对话双方有打算做某事.对话有几个情境：
个人计划类：
1、改变原计划
Then we have to do sth instead of going to doing something.
So we have to do sth instead.
2、坚持原计划
It doesn't matter. we can do sth (by another tools or in other way)
他人计划类
同上述缘由.改变或坚持计划.