Which musical composition uses retrograde as a means of direct musical representation in its text?

When was the treatise Musica enchiriadis written?

a) during the middle or second half of the 9th century b) approximately 1100 c) 1163 d) sometime between 1245 to 1255

Entasis relates to this part of a Greek temple:

a. the stylobate b. the column c. the triglyph d. the pediment