The "S" in the name of this exercise indicates that it features a secondary rhythm figure.
Secondary figures are an evolution of primary figures where the first event has been removed by a rest or a tie.

IN THIS CASE

It took thousands of years for this evolution to take place.

This figure is the secondary version of the master figure of the division by four.
In public culture, it is less than a thousand years old.

It is very frequently used.

You will see it often in classical music.

The secondary figures can be written in two different ways:

•With a rest at the beginning

•Preceded by a tie

Using a rest prevents any syncopation.

In the case of a tie, having a syncopation depends on the preceding figure.

In this table, all the starting points for the ties are weaker than their arrival on the following beat, except for the quarter note.