to fit the instruments that will be playing the piece
to fit the instruments that will be playing the piece.
The correct answer is: to fit the instruments that will be playing the piece. Key signatures are used to determine the set of notes that are generally played in a piece of music. Different instruments have different ranges and capabilities, so selecting the appropriate key signature helps ensure that the music is playable on those instruments. For example, a key signature with many sharps or flats may be better suited to a piano or a string instrument, while a simpler key signature may be more suitable for a brass instrument. Therefore, when choosing a key signature, it is important to consider the instruments that will be used to perform the piece.