The correct answer is do re mi. A music scale has all the different notes that one can sing, for example. The first three notes will be do, which is the lowest, re, which is a bit higher, and mi, which is a bit higher. You can also think of a scale as a staircase. Each note has its own step, and each time you go up a step, your voice gets a bit higher. Do will be the first step, then re, then mi, and so on and so forth.