Separation of powers refers to the division of government responsibilities among different branches to prevent any one branch from gaining too much power. In the context of your question, the following responses are examples of separation of powers:
- The legislative branch overriding a veto (this is an example of the legislative branch exercising its power to check the executive branch)
- The legislative branch approving a presidential appointment (this is another example of the legislative branch exercising its power to check the executive branch)
The other two options (collecting taxes and regulating trade) are responsibilities typically associated with the legislative branch, but they do not illustrate the concept of separation of powers.