Sentence:  If the antiphon comes to an end with the “Praeparatio” <WSD>trope</WSD>, a musical difficulty is presented by the <WSD>trope</WSD>'s cadence. Although the antiphon is in the E-plagal mode and the first three <WSD>trope</WSD> elements cadence on E, this <WSD>trope</WSD> cadences on G, a rare cadence tone in this mode. 
Meaning of the word marked with <WSD> tags:  A short cadence at the end of the melody in some early music.