Which of the following most contributed to the rise of Sumer?

A)agriculture
B)trade
C)military conquest
D)monotheism

Is the answer B? Please help, I'm not sure.

Your answer may be right in the later days of Sumer. However, I think there's a better answer. What had to come before the Sumerians could engage in much trade? Please check your text and this article.

http://www.seal-pa.org/ms/staff/dlongwell/Shared%20Documents/Mesopotamia/The%20Rise%20of%20Sumer.pdf