What was unusual about Guillaume de Machaut's most famous composition?

A. The Messe de Nostre Dame was monophonic.

B. The Messe de Nostre Dame was the first complete musical setting of the Proper sections of the Roman Catholic Mass.

C. The Messe de Nostre Dame was the first composition by a composer of the Notre Dame school.

D. The Messe de Nostre Dame was the first complete musical setting of the Ordinary sections of the Roman Catholic Mass.