Which of the following terms means "always" or "continuously" in music?

The term that means "always" or "continuously" in music is "sempre." This term is often used to indicate that a certain musical instruction should be maintained throughout a piece or section of music without interruption. For example, if a composer writes "sempre legato," it indicates that the performer should play in a smooth, connected manner continuously throughout the passage.

In contrast, the other terms have different meanings. "Simile" instructs the performer to continue in a similar manner to what has previously been played, but does not imply continuous action in the same way as "sempre." "Sforzando" refers to a sudden and strong emphasis on a note or chord. "Sostenuto" means sustained, indicating that notes should be held with a certain length but does not convey the idea of continuous action as "sempre" does. Therefore, "sempre" is the most accurate choice for conveying "always" or "continuously" in music.