A.rules intended to ensure that at least one nurse is assigned for every four patients put through triage in a hospital emergency room

B.rules with the intent of ensuring one nurse at least to be assigned for every four patients to be put through triage in a hospital emergency room

C.rules intending to ensure at least one nurse is assigned for every four patients in a hospital emergency room put through triage

D.with the intent of ensuring that at least one nurse should be assigned for every four patients in a hospital emergency room that are put through triage

E.and this is intended to ensure one nurse at least to be assigned for every four patients put through triage in a hospital emergency room

My questions: What's the function of rules in the clause here? How to use ensure?

Anyone can explain it to me? Thanks!