The correct answer is B. A sudden accent
Step-by-step explanation:
In music, sf stands for sforzando or sforzato that refers to playing a note or set of notes with more intensity or accent. This along with others such as crescendo or diminuendo belong to techniques used in music to provide rhythm, emphasize certain sections and have musical variety. Additionally, the sforzando differs from other variations because it is usually sudden accented notes. This means sf indicates a sudden accent in music.