(a) Common problems of the teeth includes dental caries (tooth decay) and bleeding gums. 

The two rules of dental hygiene are: 

1. The teeth and gums must be cleaned throughly after every meal, or atleast twice a day. Regular brushing with a fluoride toothpaste, flushing and massaging the gums are effective ways to prevent decay and disease. 

2. Rinse the mouth nicely after each meals; it possible the gargles should be done with the lukewarm water. 

(b) A genetic disease is an illness caused by one or more abnormalities in the genome, especially a condition that is present from birth. Most genetic disease are quite rare and affect one person in every several thousands or millions. Genetic disorders may or may not be heritable, i.e., passed down from the parents genes. In non-heritable genetic disorders, defects may be caused by new mutations or changes to the DNA. 

(c) The three diseases spread by bacteria are: 

1. Bacterial meningitis 

2. Toxic shock syndrome 

3. Paratyphoid fever. 

(d) The three points to prevent obesity are: 

1. Appetite: Eat when you are really hungry, avoid eating again and again and eat without feeling hungry. To have proper appetite, it is compulsory to perform some physical activity. 

2. Age Factor: As the age increases, there should be some changes in the eating habits. At childhood eat more proteins and in young age proper amount of carbohydrates, fat and proteins should be consumed and in the old age less and light food should be taken for the easy digestion. 

3. Punctuality: Eat at a proper time and also eat less at night to avoid constipation, do not over eat.