Concept:Here we need the
opposite (antonym) of the underlined word. To
infringe a rule means to break it or disobey it.
Solution:The opposite of breaking a rule is keeping or following it, which is what
observed means here (to observe a rule = to obey it).
Violated means the same as infringed (a synonym, not an opposite).
Changed means altered, and
formulated means made or drawn up; neither is the opposite of breaking a rule.
Key point: Questions 26 to 30 of this paper ask for the word opposite in meaning. The old key gave (B) violated, which is the synonym, so it is wrong; the antonym is (A) observed.
Answer:Option A (observed)