Final answer:
You should check your mirrors before you change lanes to ensure safe driving.
Step-by-step explanation:
According to proper driving practices, you should check your mirrors before you change lanes. This ensures that you have a clear understanding of your surroundings and can make safe and informed decisions. Checking your mirrors allows you to be aware of other vehicles around you and helps prevent collisions or accidents.
For example, if you are driving on a freeway and need to change lanes, you should check your rearview mirror to see if there are any vehicles approaching from behind. Additionally, you should check your side mirrors to make sure there are no vehicles in your blind spots. By checking your mirrors before changing lanes, you are able to assess the situation and make a safe maneuver.
Therefore, the correct answer to the question is (a) before you change lanes.