This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to protect your back while moving
Use a cart or a hand truck to push heavy objects whenever possible.
Be sure to push heavy objects instead of pulling.
Pushing will use stomach muscles and limit the strain on your back.

OPT:
(I). Keep your knees and torso moving in the same direction. Do not twist or turn while you are pushing an object.;
(II). Sit on one of the carts, if possible. If you have smaller wheels, be sure that they are 4-6 inches (10.2-15.;
(III). Use a regular backpack for moving heavy objects. Pulling heavy objects will decrease its impact on your back.;
(IV). Push carefully, as small items can't be pushed far enough at a time. Use the brakes when at the end of a stair column, and the sensor when at the other.;
The answer is:
(I).