You should change your tyres when ___

What this question teaches

For the question "You should change your tyres when ___", the correct answer is "Both A and B." because it is the option that best matches the traffic rule or safest action being tested in this question; the other choices such as "The thickness of the tread surface is less than 1.6mm." and "The tyre is bald or punctured." do not fit the rule as well.