To answer the question regarding what contributed to the increased economic and military power of the Sumerians, we can look at the potential causes listed:
- A series of highly strategic army leaders
- The development of bronze to make weapons
- A standing army of many trained soldiers
- The formation of alliances with other city-states
In this context, the best response to place in the "Cause" area would be B: The development of bronze to make weapons. This advancement greatly enhanced the military capabilities of the Sumerians.
You can structure it as follows:
Cause: The development of bronze to make weapons
Effect: Increased economic and military power
If you want to include other contributors, you could add them as well:
- A series of highly strategic army leaders
- A standing army of many trained soldiers
- The formation of alliances with other city-states
Those would also be relevant to explaining the increased economic and military power but start with the most direct cause.