The correct answer is: d. Motet.
The motet is a polyphonic composition born in the 13th century, made for singing at mass as a Latin religious choral composition, with biblical texts commonly. Until the 17th century it remained as one of the most important musical forms of polyphonic music. It was also characterized for its various melodies.
In the 15th century and the 16th century it expanded as a polyphonic vocal piece without instrument backing, a capella, with dynamically contrasting vocal lines with a imitative and dramatic character. It was one of the prominent polyphonic forms of Renaissance music.