A, Xiaoya rarely eats every day during adolescence, and only eats some fruits to lose weight, which will lead to malnutrition. The correct way is to strengthen exercise properly; Pay attention to a balanced diet and don't eat too many sweets; The ratio of three meals a day is appropriate, and A is wrong;

B, the general measures to prevent infectious diseases are to control the source of infection, cut off the route of transmission, and protect susceptible people; Often bask in the quilt can effectively prevent infectious diseases, that is, cut off the route of transmission. B is correct;

C, smoking, respiratory mucosa is easily damaged, smokers are prone to chronic bronchitis, lung cancer and other diseases; Smoking can lead to decreased lung function; Smoking can damage the nervous system, make people's memory decline, premature aging, C error.

D, after injection of tetanus vaccine, it will stimulate human lymphocytes to produce a special protein against tetanus virus. This protein is called antibody. Antibodies can help the human body to remove or kill the corresponding pathogens that enter the human body. D is wrong.

Therefore, choose: B.