Question

the president leads the military, but congress can refuse to declare war. which arrow stands for this check?

Explanation:

This problem relates to the system of checks and balances in the US government, specifically the legislative (Congress) checking the executive (President) on war - making power. In the diagram, the arrows between the branches represent checks. The check here is Congress (Legislative) checking the President (Executive) regarding war declaration. So the arrow from Legislative to Executive (or the arrow that shows Congress's check on the President's military - related power) is the one we need. Assuming the diagram has the Legislative (Congress - related) circle, Executive (President - related) circle, and the arrows between them, the arrow from Legislative to Executive (or the arrow that represents Congress's refusal to declare war checking the President's military leadership) is the answer. If we consider the standard checks and balances diagram, the arrow from Legislative (Congress) to Executive (President) for this check.

Answer:

The arrow from the Legislative (Congress - represented) circle to the Executive (President - represented) circle (assuming the diagram's labels: if the left circle is Legislative, top is Executive, then the arrow from left to top that represents Congress's check on the President's war - making/military leadership).