What attitude does the author hold towards aspirin

A．some tree bark and leaves could be used as aspirin
B．some tree bark and leaves had certain medical effects
C．aspirin was a good pain killer
D．aspirin could cure arthritis

A．To point' out we have greatly improved our reading methods.
B．To explain how silent reading developed.
C．To illustrate the advantages of silent reading over reading aloud.
D．To criticize the mass media.