B   

 The most common mistakes __________(lead) to a bad back are poor body mechanics and unhealthy habits. How you move objects, your posture, not stretching before exercising and the wrong kind of shoes all contribute to one of the most common medical problems today. Back pain affects eight out of 10 people in their lifetime, according to the National Institutes of Health.    Dr. Douglas Won, founder and director of Minimally Invasive SpineCARE and Star Medical Center in Plano, Texas, offers some tips to improve back health:    First, maintain proper body mechanics:

Stretch __________ exercising or doing any tough activity. Push heavy objects across the floor instead of pulling or lifting them.

__________lifting is necessary, lift with your knees, not your back.

Avoid sudden movements and "twisting" motions when carrying objects--even a bag of groceries can do serious harm when __________(handle) improperly.

Maintain good posture as often as possible. When standing, your weight__________ be balanced smoothly and regularly on both feet to avoid injuring your muscles and joints.

Wear proper shoes. High-heeled shoes are common criminals, but even tennis shoes can be __________ problem if they don't provide you with proper support.

Next, adopt healthy habits:

Exercise regularly: The best programs for back health include basic __________ (strengthen) and cardiovascular (心血管的) exercises.

Reduce stress: When stressed, the body tightens __________ muscles. This can result in spasms (痉挛), "muscle twists" and stressed nerves that are painful and can lead to more serious problems.