The tone of the author's discussion of the blues is ______.

A．The demand for luxury goods was limited in French.
B．Industrial Revolution was the result of the interaction of various factors.
C．French people were engaged in industry and commerce before the Industrial Revolution.
D．Coal was very important to people's life before the Industrial Revolution.

A．Jazz places more emphasis on Afro-American culture than does the blues.
B．Jazz changes the attitudes of white musicians toward Afro-American culture.
C．Jazz is based on the blues attitude, but expressed in comprehensible manners to white musicians.
D．Jazz must be understood in order to be played, whereas the blues must be learned.