Questions 17 to 20 are based on a lecture about four categories of music. You now have 20 seconds to read Questions 17 to 20.

What kind of instruments are used in rock music

A．by direct intervention in the pricing of goods and services
B．by means of money and the price mechanism
C．by keeping a watchful eye on relative price changes
D．by fixing prices in specific industries

A．Because it enables the developed countries to control the international market.
B．Because it destroys the economic balance of the poor countries.
C．Because it violates the national boundaries of the poor countries.
D．Because it inhibits the industrial growth of developing countries.