when do we use capital letter

when do we use capital letter when we use public document ,where do we see them we do not know when man first began to use salt,but we do kn what part of a watch do we use when we greet someone 请老师批改When we use the word “creation”,we do not simply mean “ what part of a watch do we use when we greet someone ? 英语翻译We do not know when man first began to use salt,but we d 改为被动语态I sent a letter to you last month Do we use it for coo 改为被动1、I sent a letter to you last month.2、Do we use it for c capital letter you know When do you use a computer?英语翻译 When do you usually use cell phones?