Final answer:
The correct answer to the question is b) Unison, which is what a conductor uses to begin a piece with the orchestra playing or singing the same note simultaneously.
Step-by-step explanation:
The question, "U is for one of these, with which a conductor may begin a piece," refers to how a conductor might initiate an orchestral performance. The options given pertain to music, suggesting that the correct answer must be a musical term or object that a conductor would use. The correct answer is b) Unison, which indicates a musical performance where all the instrumentalists or singers start the piece by playing or singing the same note simultaneously. This creates a uniform sound that sets the tone for the piece. It is a common practice for orchestras to start a performance in unison to ensure that everyone is tuned to the same pitch. The unison provides a clear starting point for the musicians and can set the stage for the rest of the performance. Therefore, "U" is for unison, which is what a conductor uses to begin a piece. The other options provided, such as ukulele, are musical instruments but are not related to the act of initiating an orchestral piece by a conductor in the context of the question.