The correct answer is "da capo sign." The da capo sign is a musical expression that means "from the beginning." It directs the performer to go back and repeat the music starting from the beginning. This sign is often used in sheet music to indicate a return to the opening section or a previous part of the music. To determine the answer, you can analyze the options and their definitions. The half cadence is a musical phrase that ends on the dominant chord, but it does not indicate a return to previous music. A key signature is a collection of sharps or flats at the beginning of a piece of music, but it does not specify a return to previous music. On the other hand, an authentic cadence is a chord progression from the dominant to the tonic, but it also does not directly indicate a return to previous music. Therefore, the answer must be the da capo sign, which is the musical symbol specifically used for this purpose.
