Going on a diet: A calorie is a unit for measuring the amount of energy food

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the following numbered blanks.
GOING ON A DIET

${\,\,\,\,\,\,\,}$ A calorie is a unit for measuring the amount of energy food will produce. The average person needs about 1,800 calories per day to (i) ________ healthy. Without energy, the heart cannot pump blood through blood vessels and the organs cannot function.

${\,\,\,\,\,\,\,}$ You (ii) ________ weight because you consume more calories a day than your body requires. The only way to lose weight is to reduce the number of calories you consume. This is the basic principle behind most diets.

${\,\,\,\,\,\,\,}$ (iii) ________, diets don't work for most people. It's not that they don't lose weight: they do, but when they (iv) ________ the diet, the kilos creep back. The key to losing weight and maintaining weight loss is a sensible diet and exercise plan. You need to work out how to eat fewer calories than you actually consume. You should also exercise daily so you can use up calories. Burning 250 or 500 calories per day can (v) ________ a big difference. Try riding an exercise bike while you are watching TV or climbing the stairs rather than taking the lift. Persuade someone to exercise with you; exercise is a lot easier if done in company.