Final answer:
When entering a freeway, you should check traffic using rearview mirror, side mirrors, and checking blind spots.
Step-by-step explanation:
When entering a freeway, it is important to check traffic using all of the above options: rearview mirror, side mirrors, and checking blind spots. The rearview mirror helps you see what is happening behind your vehicle, the side mirrors help you see what is happening on the sides of your vehicle, and checking blind spots helps you see any vehicles that may be in your vehicle's blind spots.