The examples that illustrate separation of powers are:
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The legislative branch approving a presidential appointment - This shows the legislative branch exercising its powers in relation to the executive branch.
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The legislative branch overriding a veto - This demonstrates how the legislative branch can check the powers of the executive branch.
The other options, "The legislative branch collecting taxes" and "The legislative branch regulating trade," do not specifically highlight the interaction between different branches of government, and therefore do not exemplify the concept of separation of powers as clearly as the first two options.