Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

  Have your parents ever scolded you for not sitting up straight during family meals or other occasions? This may become extremely annoying at times, but they are not wrong. Your posture, the way you hold your body when you're sitting or standing, is the foundation of your body movements, and can determine how well your body adapts to the stresses on it. These stresses can be things like carrying weight or sitting in an awkward position. If your posture isn't optimal, your muscles have to work harder to keep you upright and balanced. Some muscles will become tight and inflexible. Others will be inhibited. Over time, these dysfunctional adaptations may negatively affect your body's ability to deal with the forces on it. Poor posture also puts extra pressure on your joints and ligaments, increases the likelihood of accidents, and makes some internal organs, like your lungs, less efficient. Researchers have linked poor posture to scoliosis, tension headaches, and back pain, although it isn't the only cause of any of them. Bad posture can even influence your emotional state and your sensitivity to pain. So there are a lot of reasons to aim for good posture. What does good posture look like? When you're standing, you should be able to draw a straight line from a point just in front of your shoulders, to behind your hip, to the front of your knee, to a few inches in front of your ankle. This keeps your centre of gravity directly over your base of support, which allows you to move efficiently with minimal fatigue and muscle strain. If you're sitting, your neck should be vertical and not leaning forward, your shoulders should be relaxed, your knees should be at a right angle, and your feet should be flat on the floor. (Adapted from ed.ted.com)

What is the passage mainly about?