Read the procedural text.

6 Step procedural text titled Flat Tires with a diagram of a car and instructions how to change a flat tire. Step 5, Place blocks in front of and behind the tire that is located diagonally from the flat tire.

What is the main idea of step 5 in the procedure?

to make sure the engine is turned off when using the jack
to alert other drivers that you are about to change a tire
to secure the car so it does not roll while changing the tire
to make it easier to move the car while using the jack