Your studies must be the bestone

Your studies must be the bestone The girl must be your sister ,______she? You must have returned you your Dept for your studies. You must be the driver等于Must be your driver吗 The book must be s____ in your room. 英语翻译your draft must be accompanied by the following document Your account name must be The girl under the tree must be your sister.(变否定句）如何改写? It must be very interesting in your way to the best,which is 英语：The book must be your mother's(改为否定句） It must be tough to have the champion cup in your sights,onl The key must be in your pocket.——_____填什么?