24（）

单项选择题The best title for this passage is（）

A．New Light on the Cause of Cancer
B．The Newest Theory on the Nature of Viruses
C．Viruses and Cancer
D．On the Nature of Life

单项选择题According to the passage, a barter economy can lead to（）

A．rapid speed of transaction
B．misunderstanding
C．inflation
D．difficulties for the traders