Consider the correct statement about asthma among the following?

Asthma is a medical condition in which a person's airway is inflamed, swells, narrows, and starts producing extra mucus that makes difficulty in breathing. 

It may include symptoms like difficulty in breathing, chest pain, wheezing, and coughing. There is no complete cure for asthma. we can prevent this by avoiding foreign particles such as allergens and irritants, and by the use of inhaled corticosteroids. By reducing the risk of exposure to some allergens, like dust, and pollen grains, asthma may delay. Children living in cities or crowded areas have more possibility of exposure of allergens, dust, thus have higher risk of asthma.

Therefore the correct statements about asthma are children in metropolitan cities are  this is commonly affected by asthma and allergies, there is no cure for asthma and the children who grow up in crowded urban areas may have higher rates of asthma and allergy.

Hence the correct answer is option D.