Why was trade important to sumerian city-states

Which of the following discoveries would be most likely to cause a scientific paradigm shift? a. the discovery of more rings around uranus b. the discovery of a new pathogenic virus transmitted by mosquitoes c. the discovery that a dormant volcano is showing signs of activity d. the discovery of a new species of salamander in the amazon rainforest e. the discovery that excess heat is radiating from the center of the earth and causing global climate change