Explanation:
Is a non-aggression pact or neutrality pact is a treaty between two or more states/countries that includes a promise by the signatories not to engage in military action against each other. Such treaties may be described by other names, such as a treaty of friendship or non-belligerency.
The best answer for the blood vessels' valves would be these are veins that would then help in preventing the back flow of blood because the walls have small muscle to pump the blood back to the heart.Hope this is the answer.
If you're meaning like to check if someone's respiratory system is working right you'd want to find a pulse. If you find there's no pulse you should start chest compressions and call 911 continuing to do chest compressions
