According to the passage, background music is so widespread because it can ______.

A．They are used to express thoughts only.
B．They can be spoken, but can not be written down.
C．They are simply sounds.
D．They are not completely known to the world.

A．The more we read and learn, the more learned we will become.
B．The more we read and learn, the more confused we will grow.
C．The more we read and learn, the more honorable we will be.
D．The more we read and learn, the more numbers we know.