Question

if something happens to the vice president, the president can pick a replacement. but congress can accept or reject this pick. which arrow stands for this check?

Explanation:

The problem is about the system of checks and balances in the US government, specifically the legislative (Congress) checking the executive (president's pick for vice - president replacement). In the diagram, the arrow from Executive to Legislative (or vice - versa? Wait, no: the president (Executive) makes a pick, Congress (Legislative) checks it. So the arrow that represents Congress's check on the Executive's pick would be the arrow from Executive to Legislative? Wait, no, the check is Congress accepting or rejecting, so the flow is Executive (president's action) to Legislative (Congress's check). But looking at the diagram, the circles are Executive, Judicial (maybe the left one), and Legislative (right). The checks and balances: when the president (Executive) nominates (for vice - president replacement), Congress (Legislative) has the power to accept or reject. So the arrow that goes from Executive to Legislative (the one where Executive is the source and Legislative is the target, representing the president's action being checked by Congress) or maybe the reverse? Wait, no, the check is Congress's power over the Executive's action. So the arrow that stands for Congress's check on the Executive's pick would be the arrow from Executive to Legislative (the one where the Executive initiates the action, and Legislative checks it). But in the diagram, the arrows: let's assume the right circle is Legislative. The arrow from Executive to Legislative (the green arrow going from Executive down to Legislative) would represent the president's pick (Executive action) being subject to Congress's (Legislative) approval or rejection. So the arrow from Executive to Legislative (the one where Executive is the origin and Legislative is the destination) is the one that stands for this check.

Answer:

The arrow from the "Executive" circle to the "Legislative" circle (the green arrow originating from Executive and pointing towards Legislative)