I don't know when we shall leave for Moon Bay.(改为简单句)为什么用to?

I don't know when we shall leave for Moon Bay.(改为简单句)为什么用to? I don't know when we shall start.(改为简单句) I don't know ____ _ I don't know when we shall meet again .(改为简单句） We don't know when we shall leave for Nanjing. I don't know when we should leave for Nanjing. I want to know when we are going to leave（改为简单句） 英语改写句子,急用I don’t know when i shall start the work （改为简单句）I d I don't know when we will begin the work.改为简单句. I don't know when to leave I do not know when we shall leave for Nanjing. We don`t know when we shall start .(改为to do 的结构） We don`t kn I don't know when we will leave the city.(同义句） I don't know（