Which of these refer to emphasis on a single musical note?
- syncopation
-tempo
-accent
-upbeat

accent

Explanation:

A pure and simple succession of heartbeats does not yet seem sufficient to set a rhythm.

This is where the first essentially musical rhythmic factor intervenes: the accents.

In the sound of the alarm clock, it is easy to see that the tics are a bit more pronounced than the taps.

Thus, instead of a simple succession of equal pulsations, we actually have a series of pulses of the same duration, but grouped two by two, the first one always a little stronger, accentuated:

These accents, the tics of our example, give an elementary principle of order to the succession of times: the groupings of two pulsations, one strong, the other weak.

by acting roughly or something dramatic happening in the story.