What note sequence is indicated by a 'Trill' ornament?

A 'Trill' ornament is a musical technique where a performer rapidly alternates between a written note and the note that is a scale step above it. This technique adds expressiveness and decoration to the melody.

In this case, option B captures this definition perfectly by stating that the trill consists of the written note alternating with the note above it. This usage typically occurs in the context of classical music and is indicated by the symbol 'tr'.

Other options do not accurately reflect the nature of a trill. For instance, option A suggests using the note below, which is characteristic of a different ornament known as a 'turn.' Meanwhile, option C implies that both the notes above and below would be involved simultaneously, which is not how trills are typically executed. Lastly, option D suggests repeating the written note and then the note below, which also describes a different ornamentation technique rather than a trill.