Question

altering or removing a vehicles emission control device... should never be done. is recommended. should only be done when making repairs, replacing it, or converting it to a lower emission device.

Explanation:

Vehicle emission control devices are crucial for reducing harmful pollutants. Altering or removing them without proper reasons (like repairs, replacements, or conversions to lower - emission devices) can lead to increased pollution. It is against environmental regulations and good practice in most cases.

Answer:

should only be done when making repairs, replacing it, or converting it to a lower emission device.