The answer is letter D.
Communicable diseases are also known as infectious or contagious diseases. They may come from food, water, animals, another person, or anything that comes from the environment. Airborne viruses, bacteria, blood, and bodily fluids can cause the spread of these diseases. The most common communicable disease is the flu, which can easily spread in an enclosed environment with a recycled circulating air (e.g. air-conditioning). Infectious disease caused by blood contact like HIV/AIDs are also dominant in society.